msm_fb: Correct the chroma offset calculations for Yamato format

In the PPP blit operations, when the source image format is
Yamato, there is chroma offset calculations going wrong in
the case when a frame is split into parts and blit is done
separately. Correct the chroma offset calculations in this
case.

CRs-fixed: 366908
Change-Id: I867024632fda9f64a569150e0b6389d55614cd3a
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>