mako: display: change color value to displayed in case of underflow

In case of data underflow, MDP display specific color on lcd.
Due to data underflow rarely happen during display on/off,
we can see unintended blue screen at that time.
So this patch changes this underflow control color from blue to black
for hiding unintended blue image displaying during display on/off.

Change-Id: I26910065b5210a2571125d25f3f1b41a67ba1c1c