CHROMIUM: MALI: fix async wait for fence

Adding callback can fail if the fence is already signaled. Handle it
properly and return fence status.

BUG=b:64852540
TEST=as described in bug

Change-Id: Ia3d4f2818290bbe4d322310bd92c48d745ea26d9
Signed-off-by: Dominik Behr <dbehr@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/651140
Commit-Ready: Douglas Anderson <dianders@chromium.org>
Tested-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
(cherry picked from commit ae0c3949493cf978833c37ca65ef68f3ddc401e0)
Reviewed-on: https://chromium-review.googlesource.com/655538
Reviewed-by: Douglas Anderson <dianders@chromium.org>

• drivers/gpu/arm/midgard/mali_kbase_softjobs.c[diff]