Make SDL_SetError and friends unconditionally return -1.

This lets us change things like this...

    if (Failed) {
        SDL_SetError("We failed");
        return -1;
    }

...into this...

    if (Failed) {
        return SDL_SetError("We failed");
    }


 Fixes Bugzilla #1778.

src/thread/psp/SDL_syscond.c

@@ -82,8 +82,7 @@ int
 SDL_CondSignal(SDL_cond * cond)
 {
     if (!cond) {
-        SDL_SetError("Passed a NULL condition variable");
-        return -1;
+        return SDL_SetError("Passed a NULL condition variable");
     }
 
     /* If there are waiting threads not already signalled, then
@@ -107,8 +106,7 @@ int
 SDL_CondBroadcast(SDL_cond * cond)
 {
     if (!cond) {
-        SDL_SetError("Passed a NULL condition variable");
-        return -1;
+        return SDL_SetError("Passed a NULL condition variable");
     }
 
     /* If there are waiting threads not already signalled, then
@@ -164,8 +162,7 @@ SDL_CondWaitTimeout(SDL_cond * cond, SDL_mutex * mutex, Uint32 ms)
     int retval;
 
     if (!cond) {
-        SDL_SetError("Passed a NULL condition variable");
-        return -1;
+        return SDL_SetError("Passed a NULL condition variable");
     }
 
     /* Obtain the protection mutex, and increment the number of waiters.

src/thread/psp/SDL_sysmutex.c

@@ -78,8 +78,7 @@ SDL_mutexP(SDL_mutex * mutex)
     SDL_threadID this_thread;
 
     if (mutex == NULL) {
-        SDL_SetError("Passed a NULL mutex");
-        return -1;
+        return SDL_SetError("Passed a NULL mutex");
     }
 
     this_thread = SDL_ThreadID();
@@ -107,14 +106,12 @@ SDL_mutexV(SDL_mutex * mutex)
     return 0;
 #else
     if (mutex == NULL) {
-        SDL_SetError("Passed a NULL mutex");
-        return -1;
+        return SDL_SetError("Passed a NULL mutex");
     }
 
     /* If we don't own the mutex, we can't unlock it */
     if (SDL_ThreadID() != mutex->owner) {
-        SDL_SetError("mutex not owned by this thread");
-        return -1;
+        return SDL_SetError("mutex not owned by this thread");
     }
 
     if (mutex->recursive) {

src/thread/psp/SDL_syssem.c

@@ -105,8 +105,7 @@ int SDL_SemWaitTimeout(SDL_sem *sem, Uint32 timeout)
                case SCE_KERNEL_ERROR_WAIT_TIMEOUT:
                        return SDL_MUTEX_TIMEDOUT;
                default:
-                       SDL_SetError("WaitForSingleObject() failed");
-                       return -1;
+                       return SDL_SetError("WaitForSingleObject() failed");
 	}
 }
 
@@ -142,14 +141,12 @@ int SDL_SemPost(SDL_sem *sem)
 	int res;
 
 	if (sem == NULL) {
-		SDL_SetError("Passed a NULL sem");
-		return -1;
+		return SDL_SetError("Passed a NULL sem");
 	}
 
 	res = sceKernelSignalSema(sem->semid, 1);
 	if (res < 0) {
-		SDL_SetError("sceKernelSignalSema() failed");
-		return -1;
+		return SDL_SetError("sceKernelSignalSema() failed");
 	}
 
 	return 0;

src/thread/psp/SDL_systhread.c

@@ -54,8 +54,7 @@ int SDL_SYS_CreateThread(SDL_Thread *thread, void *args)
 					       priority, 0x8000, 
 					       PSP_THREAD_ATTR_VFPU, NULL);
 	if (thread->handle < 0) {
-		SDL_SetError("sceKernelCreateThread() failed");
-		return -1;
+		return SDL_SetError("sceKernelCreateThread() failed");
 	}
 
 	sceKernelStartThread(thread->handle, 4, &args);