drm/vc4: perfmon: Add missing mutex_destroy

vc4_perfmon_open_file() will instantiate a mutex for that file instance,
but we never call mutex_destroy () in vc4_perfmon_close_file().

Let's add that missing call.
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20220711173939.1132294-67-maxime@cerno.tech

drivers/gpu/drm/vc4/vc4_perfmon.c

@@ -133,6 +133,7 @@ void vc4_perfmon_close_file(struct vc4_file *vc4file)
 	idr_for_each(&vc4file->perfmon.idr, vc4_perfmon_idr_del, NULL);
 	idr_destroy(&vc4file->perfmon.idr);
 	mutex_unlock(&vc4file->perfmon.lock);
+	mutex_destroy(&vc4file->perfmon.lock);
 }
 
 int vc4_perfmon_create_ioctl(struct drm_device *dev, void *data,