disp: msm: dsi: fix physical size truncation of large panel

Panel's physical width/height larger than 255mm is getting
truncated due to type conversion into smaller type.

Change-Id: I826fb2db542146c07d8379951563430b7da8288c
Signed-off-by: Rajeev Nandan <rajeevny@codeaurora.org>
Signed-off-by: Satya Rama Aditya Pinapala <psraditya30@codeaurora.org>