msm: mdss: Fix DSI ROI alignment read during DSI probe

Fixes a bug in reading the DSI ROI alignment values as per the
property description.

Change-Id: Ieffa48891f4f9219951b6e90009369db993791a7
Signed-off-by: Jeykumar Sankaran <jsanka@codeaurora.org>
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>