drivers/rtc/s3c24x0_rtc.c: fix GCC 4.6 warnings

Fix:
s3c24x0_rtc.c: In function 'rtc_get':
s3c24x0_rtc.c:67:53: warning: variable 'a_armed' set but not used
s3c24x0_rtc.c:67:45: warning: variable 'a_year' set but not used
s3c24x0_rtc.c:67:38: warning: variable 'a_mon' set but not used
s3c24x0_rtc.c:67:30: warning: variable 'a_date' set but not used
s3c24x0_rtc.c:67:22: warning: variable 'a_hour' set but not used
s3c24x0_rtc.c:67:15: warning: variable 'a_min' set but not used
s3c24x0_rtc.c:67:8: warning: variable 'a_sec' set but not used
[-Wunused-but-set-variable]

Signed-off-by: Anatolij Gustschin <agust@denx.de>