msm: kgsl: Use kgsl_check_timestamp when possible

Instead of manually checking the retired timestamp against a known
value, use kgsl_check_timestamp to do it instead.  Yay code reuse.

Change-Id: Ic0dedbad056b068da983677367899ec4d5663c53
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>