msm: kgsl: Reschedule idle work in case transition to idle state fails

Reschedule the idle work in case transition to idle state is rejected
because the GPU is busy. This change avoids the condition where
transition to NAP state gets rejected due to a pending IRQ which is
currently getting served by IRQ handler because of which GPU remains
in active state even when GPU is idle.

Change-Id: I472a30b6a0e83cdd6957ed12eaa39d0c7731fcb5
Signed-off-by: Deepak Kumar <dkumar@codeaurora.org>