msm: mdss: Reverting the fix for spurious interrupt.

Reverting the fix for spurious interrupt to force the irq mask to 0.
It is seen that the vsync interrupt is not disabled sometimes
during idle screen scenario causing the mdp clock to be active always.

Change-Id: I33305ef105c668d0a0d14d247ae53ce67aba6113
Signed-off-by: Sravanthi Kollukuduru <skolluku@codeaurora.org>