drm/msm/sde: fix undervote due to wrong condition check

Current driver assumes that AB and IB votes scale
up and down at the same time, but in some corner
cases it is possible that the IB vote scales up
while the AB vote is going down; in those cases
driver must update the IB vote to account for the
upscaling, but should not update the AB vote until
the new HW configuration has taken effect.
Fix the above issue by separating the AB and IB
vote, so the driver can scale each value
independently.

Change-Id: I0dac17f7d70c825d529e624deb0f138584b721de
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>