drm/msm: Fix submit error-path leaks

For errors after msm_submitqueue_get(), we need to drop the submitqueue
reference.  Additionally after get_unused_fd() we need to drop the fd.
The ordering for dropping the queue lock and put_unused_fd() is not
important, so just move this all into out_post_unlock.

v2: Only drop queue ref if submit doesn't take it
v3: Fix unitialized submit ref in error path
v4: IS_ERR_OR_NULL()

Reported-by:  <pinkperfect2021@gmail.com>
Fixes: f0de40a1 drm/msm: ("Reorder lock vs submit alloc")
Signed-off-by: Rob Clark <robdclark@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/536073/
Link: https://lore.kernel.org/r/20230509203041.440619-1-robdclark@gmail.com