drivers/rtc/rtc-s3c.c: fix no occurrence of alarm interrupt

The driver does not generate an alarm interrupt even though a time for
an alarm is set.

This results from disabling rtc_clk after setting the alarm time.

To generate an alarm interrupt the driver should maintain its enabled
state for rtc_clk the until alarm interrupt occurs.  This patch permits
generation of an alarm interrupt.

[akpm@linux-foundation.org: make s3c_rtc_alarm_clk_lock local to s3c_rtc_alarm_clk_enable()]
Signed-off-by: Donggeun Kim <dg77.kim@samsung.com>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>