msm: mdss: fix green line issue in video playback

Green lines were seen because of in correct initial phase and
phase step size computed with source crop, which results in over
fatching on the edges of source ROI.

Change-Id: If1477afac8b895b51c1ac9bc58b5e4da9f18a769
Signed-off-by: Ramakant Singh <ramaka@codeaurora.org>