rtc: rv3029: remove open coded regmap_update_bits

rv3029_update_bits open codes regmap_update_bits and forgets to properly
lock the register range while doing so. Use regmap_update_bits instead.

Link: https://lore.kernel.org/r/20191214221022.622482-4-alexandre.belloni@bootlin.com


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