rtc: sh: use local variables in probe() for mapping IO

No need to store the resource for the registers in the per-device struct
because we only need it during probe. Remove some unneeded unlikely()
while here and correct the type of 'regsize'.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/20250227134256.9167-17-wsa+renesas@sang-engineering.com


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