msm: mdss: Add special case for DSPP3 histogram intr shift bit

In order to enable/disable histogram interrupts, the interrupt
bit mask is programmed to the same histogram interrupt register for
all DSPPs. However, DSPP3's bit mask does not follow the typical
offset. We must add a special case for that interrupt bit shift.

Change-Id: Ia76a7eb0e56e30b657968ea776579c53ff43e390
Signed-off-by: Benet Clark <benetc@codeaurora.org>