msm: mdss: double check mdp ping pong done state

There are cases where the irq trigger may get delayed for more than
expected, in such cases the ping pong done status may have been updated
by MDP hw. Add additional check to see if this has been triggered even
though interrupt wasn't scheduled for pingpong done.

Change-Id: I4730d166d95f238f4525eab2b5c99be40b30699b
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>