xilinxfb: Don't bail if the xilinxfb platform device doesn't have any pdata

Lack of pdata is not a fatal omission.  The driver can still be used even
if we do not know the screen dimensions.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Cc: Andrei Konovalov <akonovalov@ru.mvista.com>
Signed-off-by: Antonino Daplas <adaplas@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>