msm_fb: Clean up the fix for error in y-offset check in FB driver

There is a failure observed in yres_virtual offset check and every
third frame gets skipped without an error message. Due to this high
fps is noticed in the test applications. Correct the yres_virtual
offset check.

Change-Id: Iddce0b75e0a9c466adad6eb5726203ae0586c27b
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>