msm: mdss: calculate the correct ROI for flipped panels

Calculate the correct ROI for partial update when the panels
are flipped (hflip, vflip or both)

Change-Id: If7110491ad540d7a65f7845455a657459d94485d
Signed-off-by: Vishnuvardhan Prodduturi <vproddut@codeaurora.org>
Signed-off-by: Jayant Shekhar <jshekhar@codeaurora.org>