drivers/rtc/rtc-s3c.c: fix failed first read of RTC time

Initialize the device time (if it is wrong) before registering RTC device
to fix following error message during rtc-s3c probe:

[    2.215414] rtc (null): read_time: fail to read
[    2.216322] s3c-rtc 10070000.rtc: rtc core: registered s3c as rtc1

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>