hwmon: (vt8231) Introduce a #define for the driver name and use it

hwmon: (vt8231) Introduce a #define for the driver name and use it

Make use of the cpp symbol DRIVER_NAME to set the driver's name and use
it instead of all explicit usages of the same string. Also make use of
it instead of vt8231_driver.driver.name which breaks a cyclic dependency
between vt8231_probe() and vt8231_driver that in the next commit allows
to drop some forward declarations.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20220920135617.1046361-1-u.kleine-koenig@pengutronix.de
Signed-off-by: Guenter Roeck <linux@roeck-us.net>