msm: mdss: rotator: return dst format for request match optimization

As per current implementation, every successful OVERLAY_SET IOCTL should
return destination format for that request. Now there is a driver based
optimization where if back to back OVERLAY_SET IOCTLs request same
configurations then driver avoids extra register writes. However this
optimization doesn't return correct destination format which violates the
IOCTL spec and may result in inefficiencies. Fix this by returning correct
destination format for this optimization.

Change-Id: I792e2f44f17bceb1efc7b1d389db84478581c474
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>