rtc: s3c: add missing clk control

It's missed to call clk_unprepare() about info->rtc_src_clk in
s3c_rtc_remove and to call clk_disable_unprepare about info->rtc_clk in
error routine of s3c_rtc_probe.

Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>