RTC: sa1100: Clean out ost register

These registers are used in old ioctl of UIE and PIE, now they are
emulated by rtc generic code of hrtimer, so it can be removed.

Signed-off-by: Jett.Zhou <jtzhou@marvell.com>
Acked-by: Haojian Zhuang <haojian.zhuang@gmail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>