mdss: rotator: validate rotation request ROI with img dimensions

Prevent accessing memory beyond buffer size. Prior to this check
rotator was page faulting trying to handle invalid requests, in which
offset + region of interest size was greater than the image size.

Change-Id: Ifffed0e908b29fb6e326314ec1eda148bb72db64
Signed-off-by: Terence Hampson <thampson@codeaurora.org>