watchdog: sb_wdog: release irq and reboot notifier in error path and module_exit()

irq and reboot notifier are acquired in module_init() but never released.
They should be released correctly, otherwise reloading the module or error
during module_init() will cause a problem.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Andrew Sharp <andy.sharp@lsi.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>