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@kili


Signed-off-by: Rob Clark <robdclark@chromium.org>