msm_fb: display: Program source address registers correctly

Scale filter FIR uses the adjacent pixels as part of the
processing. Source address registers should be program such that
they point to the first valid pixel so that non-ROI pixels are
ignored. This is done by making source x,y offsets to zero and
adding the computed offset to source address.

(cherry picked from commit 7bcecf0a6a6864accfa1318e33e85ad2cc23f535)

Change-Id: I4de6a6f28aee2cc9896a028164172a4c3bad950f
CRs-Fixed: 380020
Signed-off-by: Mayank Chopra <makchopra@codeaurora.org>