msm: kgsl: Modify only the pending idle timer in ISR.

mod_timer reactivates the timer even when timer is deleted using
del_timer_sync. In the ISR we should be modifying only the pending
timer. We deleted the timer using del_timer_sync, if the interrupts
are still enabled, we could be re-enabling the timer in the ISR.

There is a code path in kgsl_suspend device where we delete the timer
but disable IRQ later.This code path seems to be fixed with another
commit.

Change-Id: I1253dd3c774427e725d302d9ba13d87fad10c463
Signed-off-by: Tarun Karra <tkarra@codeaurora.org>