gallium: pipe_mutex_init() is of type void.

Both the windows and fallback versions are void already.

src/gallium/include/pipe/p_atomic.h

@@ -84,10 +84,7 @@ struct pipe_atomic {
 static INLINE void
 p_atomic_set(struct pipe_atomic *v, int32_t i)
 {
-   int ret;
-   ret = pipe_mutex_init(v->mutex);
-   if (ret)
-      abort();
+   pipe_mutex_init(v->mutex);
    pipe_mutex_lock(v->mutex);
    v->count = i;
    pipe_mutex_unlock(v->mutex);

src/gallium/include/pipe/p_thread.h

@@ -73,7 +73,7 @@ typedef pthread_cond_t pipe_condvar;
    static pipe_mutex mutex = PTHREAD_MUTEX_INITIALIZER
 
 #define pipe_mutex_init(mutex) \
-   pthread_mutex_init(&(mutex), NULL)
+   (void) pthread_mutex_init(&(mutex), NULL)
 
 #define pipe_mutex_destroy(mutex) \
    pthread_mutex_destroy(&(mutex))