rtc: ds1307: correct register offset for rx8130

While rx8130 has a register offset of 0x10 in its chip_desc, this isn't
used when regmap accesses are done. So add 0x10 to access the right
locations.

Fixes: ee0981be ("rtc: ds1307: Add support for Epson RX8130CE")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>