rtc: rzn1: Disable controller before initialization

Datasheet says that the controller must be disabled before setting up
either SUBU or SCMP. This did not matter so far because the driver only
supported SUBU which was the default, too. It is good practice to follow
datasheet recommendations, though. It will also be needed because SCMP
mode will be added in a later patch.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/r/20250526095801.35781-7-wsa+renesas@sang-engineering.com


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