- Fix fb_pan_display rejecting yoffsets that are valid if panning mode
  is ywrap.

- Add more robust error checking in fb_pan_display specially since this
  function is accessible by userland apps.
Signed-off-by: NAntonino Daplas <adaplas@pol.net>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>