msm: msm_fb: Replace wait for DMA_P with VSYNC in Pan_display Path.

This is a follow up change on gerrit 442946. Wait for DMA_P has to be
replaced with VSYNC even in Pan Display Path.

Change-Id: I8d600022cfa63f54d5b72ea5f64fc55315079b3a
Signed-off-by: Vishnuvardhan Prodduturi <vproddut@codeaurora.org>