drm: xlnx: crtc: Fix max width and height overflow
The maximum resolution supported is shown as -1x-1 in Xorg.log when
trying to run Xorg. This is occurring due to width and height variables
overflowing as they are assigned UINT_MAX instead of INT_MAX.
This patch fixes this by correcting the data types of width and height
variables and correctly assigning INT_MAX as maximum width and height.