tdfxfb: remove ypan checks done by a higher layer

These checks and assignments are done by a higher layer so remove them
from the driver.

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>