drm/msm: Pre-allocate hw_fence

Avoid allocating memory in job_run() by pre-allocating the hw_fence.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/527832/
Link: https://lore.kernel.org/r/20230320144356.803762-2-robdclark@gmail.com