drm/msm: unlock on error in get_sched_entity()

Add a missing unlock on the error path if drm_sched_entity_init() fails.

Fixes: 68002469 ("drm/msm: One sched entity per process per priority")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20211011124005.GE15188@kiliSigned-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/msm_submitqueue.c

@@ -101,6 +101,7 @@ get_sched_entity(struct msm_file_private *ctx, struct msm_ringbuffer *ring,
 
 		ret = drm_sched_entity_init(entity, sched_prio, &sched, 1, NULL);
 		if (ret) {
+			mutex_unlock(&entity_lock);
 			kfree(entity);
 			return ERR_PTR(ret);
 		}