msm: mdss: rotator: calculate the correct wb stride using img width

The width provided to mdss_mdp_get_plane_sizes, which is used for
calculate stride, was using destination region of interest
width instead of buffer image width.

Change-Id: Ib585999207860fc85adeb1a9b23a6ba31dc543e2
Signed-off-by: Terence Hampson <thampson@codeaurora.org>