msm_fb: display: fix underrun seen for some YV12 format input

Underruns seen on display because source rectangle width is
aligned to 16 before being passed to MDP. Only ystride should be
aligned, source rectangle should be passed as received.

CRs-Fixed: 329453
Change-Id: Ibb71ad316023d21ebad4c5db37fdc5e5c8acb02b
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>