drm/msm: Fix wait_fence submitqueue leak

We weren't dropping the submitqueue reference in all paths.  In
particular, when the fence has already been signalled. Split out
a helper to simplify handling this in the various different return
paths.

Fixes: a61acbbe ("drm/msm: Track "seqno" fences by idr")
Signed-off-by: Rob Clark <robdclark@chromium.org>
Link: https://lore.kernel.org/r/20211111192457.747899-2-robdclark@gmail.com


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