rtc: s5m: Check return value of s5m_check_peding_alarm_interrupt()

s5m_check_peding_alarm_interrupt() in s5m_rtc_read_alarm() gets the return
value, but doesn't use it.
This modifies using the s5m_check_peding_alarm_interrupt()"s return value
as the s5m_rtc_read_alarm()'s return value.

Cc: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: linux-samsung-soc@vger.kernel.org
Signed-off-by: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20210708051304.341278-1-nobuhiro1.iwamatsu@toshiba.co.jp