drivers/rtc/rtc-s3c.c: fixup wake support for rtc

The driver is not balancing set_irq and disable_irq_wake() calls, so
ensure that it keeps track of whether the wake is enabled.

The fixes the following error on S3C6410 devices:

  WARNING: at kernel/irq/manage.c:382 set_irq_wake+0x84/0xec()
  Unbalanced IRQ 92 wake disable

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>