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.

CRs-Fixed: 380020
Change-Id: I998fdd46f39dc67f32c422ec209da59d1add2e95
Signed-off-by: Mayank Chopra <makchopra@codeaurora.org>