msm: mdss: fix irq getting disabled when running concurrent displays

Add check to make sure there are no other active interrupts before
disabling MDP IRQ to avoid disable of interrupts.

Change-Id: Ic2bb9398dfa67d2b210f988de6648d49fd8336ac
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>