msm: kgsl: Update the dispatcher timer properly

The dispatcher timer should be updated if preemption is not in
progress. This schedules the dispatcher work in case the command
does not make progress.

Change-Id: I9ef55b12d7a4f07a3c5bba650e37453bd8f86ce3
Signed-off-by: Lynus Vaz <lvaz@codeaurora.org>