drm/client: Fix error code in drm_client_buffer_vmap_local()

This function accidentally returns zero/success on the failure path.
It leads to locking issues and an uninitialized *map_copy in the
caller.

Fixes: b4b0193 ("drm/fbdev-generic: Fix locking with drm_client_buffer_vmap_local()")
Signed-off-by: Dan Carpenter <[email protected]>
Reviewed-by: Dmitry Osipenko <[email protected]>
Reviewed-by: Thomas Zimmermann <[email protected]>
Signed-off-by: Thomas Zimmermann <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

Author: Dan Carpenter

drivers/gpu/drm/drm_client.c

@@ -355,7 +355,7 @@ int drm_client_buffer_vmap_local(struct drm_client_buffer *buffer,
 
 err_drm_gem_vmap_unlocked:
 	drm_gem_unlock(gem);
-	return 0;
+	return ret;
 }
 EXPORT_SYMBOL(drm_client_buffer_vmap_local);