drm/msm: Fix a fence leak in submit error path

drm/msm: Fix a fence leak in submit error path

[ Upstream commit 5d319f75ccf7f0927425a7545aa1a22b3eedc189 ]

In error paths, we could unref the submit without calling
drm_sched_entity_push_job(), so msm_job_free() will never get
called.  Since drm_sched_job_cleanup() will NULL out the
s_fence, we can use that to detect this case.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/653584/
Signed-off-by: Rob Clark <robin.clark@oss.qualcomm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>