nouveau: don't leak dec struct on error

This one path doesn't goto fail, so it seems to leak dec.

Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Signed-off-by: Dave Airlie <airlied@redhat.com>

src/gallium/drivers/nouveau/nouveau_video.c

@@ -553,7 +553,7 @@ nouveau_create_decoder(struct pipe_context *context,
                                &mpeg);
    if (ret < 0) {
       debug_printf("Creation failed: %s (%i)\n", strerror(-ret), ret);
-      return NULL;
+      goto fail;
    }
 
    dec->mpeg = mpeg;