rtc: rzn1: fix BCD to rtc_time conversion errors

tm_mon describes months from 0 to 11, but the register contains BCD from
1 to 12. tm_year contains years since 1900, but the BCD contains 20XX.
Apply the offsets when converting these numbers.

Fixes: deeb4b53 ("rtc: rzn1: Add new RTC driver")
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/r/20241113113032.27409-1-wsa+renesas@sang-engineering.com


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