If CONFIG_FB_DEFERRED_IO is set, but there are framebuffers
registered that does not make use of deferred io, then fsync()
on those framebuffers will result in a crash. Fix that.

This is needed for sh_mobile_lcdcfb since we always enable
deferred io at compile time but we may disable deferred io
for some types of hardware configurations.
Signed-off-by: NMagnus Damm <damm@igel.co.jp>
Acked-by: NJaya Kumar <jayakumar.lkml@gmail.com>
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>