hwmon: (smsc47m1) Mark driver struct with __refdata to prevent section mismatch

hwmon: (smsc47m1) Mark driver struct with __refdata to prevent section mismatch

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 the following section mismatch warning

	WARNING: modpost: drivers/hwmon/smsc47m1: section mismatch in reference: smsc47m1_driver+0x8 (section: .data) -> smsc47m1_remove (section: .exit.text)

that triggers on an allmodconfig W=1 build.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/57977a88a9b99b6555b227aa4994ac3df10c6490.1701957840.git.u.kleine-koenig@pengutronix.de
Signed-off-by: Guenter Roeck <linux@roeck-us.net>