msm: kgsl: Don't halt dispatcher if device is not in SUSPEND state

Add a check to make sure device actually transitioned to SUSPEND
state before halting dispatcher. kgsl_pwrctrl_change_state(device,
KGSL_STATE_SUSPEND) can return zero without actually changing
state to SUSPEND if device state is NONE or INIT.

Change-Id: I4a5a69007c71651ea2cf7fa7360c960c6856031e
Signed-off-by: Deepak Kumar <dkumar@codeaurora.org>