rtc: s5m: Remove reference to parent's device pdata

The S5M RTC driver does not use parent's device (sec-core PMIC driver)
platform data so there is no need to check for it.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20210420170244.13467-3-krzysztof.kozlowski@canonical.com