msm_fb: Fix chroma offset calculation for YUV as source format

For frame composition using MDP, fix the calculation of source
chroma offset pointer to be programmed to MDP hardware whenever
the crop 'y' value is non-zero. This prevents green lines/chroma
shift and other artifacts from being seen on the panel.

CRs-fixed: 438027
Change-Id: Id6c2a7d2c2709edd0bacfc049df360e1c0f3b90f
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>