msm: mdss: fix a racing condition in the dsi interrupt handler

At the time of dsi interrupt handler registration, there may be
a pending dsi interrupt. This can cause a dead-lock, as dsi clocks
and resources are not initialized properly yet.

Change-Id: I511d0776f5d7b500f0f32f2ae9d92ac031f8e613
Signed-off-by: Xiaoming Zhou <zhoux@codeaurora.org>