rtc: s3c: Use generic helper to get driver data

Replace of_match_node() with of_device_get_match_data(), which removes a
few lines of code from the driver.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>