rtc: sh: minor fixes to adhere to coding style

Use the BIT macro, use curly braces for else-blocks, don't split strings
over multiple lines, annotate the lock, update copyright.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/20250227134256.9167-18-wsa+renesas@sang-engineering.com


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