s3c2410_wdt watchdog driver: Locking and coding style

Kill off use of semaphores.
Fix ioctl races and locking holes.

From: Alan Cox <alan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>