watchdog: s3c2410_wdt - Fix removing of platform device

When removing the watchdog platform device, we need to
disable the access to userspace first. It makes no sense
to remove the drivers clock, irq's, ... and then disable
userspace access.
the order of removal has also been changed so that it
is the reverse of probing (this way the clock is also
disabled sooner).

Cc: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>