rtc: sh: Mark driver struct with __refdata to prevent section mismatch warning

As described in the added code comment, a reference to .exit.text is ok
for drivers registered via module_platform_driver_probe(). Make this
explicit to prevent a section mismatch warning.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20231002080529.2535610-7-u.kleine-koenig@pengutronix.de


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