drm/msm/gem: Don't queue job to sched in error cases

We shouldn't be running the job in error cases.  This also avoids having
to think too hard about where the objs get unpinned (and if necessary,
the resv takes over tracking that the obj is busy).. ie. error cases it
always happens synchronously, and normal cases it happens from scheduler
job_run() callback.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/568331/