msm: camera: reset stats irq mask

After processing stats irq, we need to reset the stats irq mask.
In the divert fail case, the stats irq mask reset is missing.
Divert fail happened on dual vfe case, which we need to
wait until second half stats buffer arrives.

Change-Id: I640aa1094b7248501daec83117166b09ac0cd860
Signed-off-by: Peter Liu <pingchie@codeaurora.org>