Wayland: Fixed missing error message if creating a custom cursor failed.

SDL_GetError() returned no error message because it was written to stderr only.

src/video/wayland/SDL_waylandmouse.c

@@ -116,8 +116,7 @@ create_buffer_from_shm(Wayland_CursorData *d,
     shm_fd = wayland_create_tmp_file(size);
     if (shm_fd < 0)
     {
-        fprintf(stderr, "creating mouse cursor buffer failed!\n");
-        return -1;
+        return SDL_SetError("Creating mouse cursor buffer failed.");
     }
 
     d->shm_data = mmap(NULL,
@@ -128,9 +127,8 @@ create_buffer_from_shm(Wayland_CursorData *d,
                        0);
     if (d->shm_data == MAP_FAILED) {
         d->shm_data = NULL;
-        fprintf (stderr, "mmap () failed\n");
         close (shm_fd);
-        return -1;
+        return SDL_SetError("mmap() failed.");
     }
 
     shm_pool = wl_shm_create_pool(data->shm, shm_fd, size);