[ARM] 4098/1: ARM: rtc_lock only used with rtc_cmos

Fix build glitches on ARM ... the only user of "rtc_lock" today is the
optional PC-style "CMOS" RTC driver, the legacy SA1100 RTC driver is
not even in the tree any more.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>