[PATCH] fix s3c24xx gpio driver (include linux/workqueue.h)

The general gpio driver includes seem to now depend on having
<linux/workqueue.h> included before they are.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>