[PATCH] null pointer dereference in appledisplay driver

Commit 40b20c25 by Len Brown introduced
a null pointer dereference in the appledisplay driver. This patch fixes
it.

Signed-off-by: Michael Hanselmann <linux-kernel@hansmi.ch>
Cc: Len Brown <lenb@kernel.org>
Cc: Greg KH <greg@kroah.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>