rtc: ds1672: remove unnecessary check

The rtc pointer is already checked earlier, it is not necessary to check it
again.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20190818215232.17320-1-alexandre.belloni@bootlin.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>