drm/msm: gpu: Only sync fences on rings that exist

The fault recovery code tries to sync fences on all possible rings
instead of only the rings that actually exist which will fault the
kernel when the number of rings are less than the maximum amount.

Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>
(cherry picked from commit 7ddae82e)