hwmon: (aspeed-g6-pwm-tacho): Make use of devm_pwmchip_alloc() function

This prepares the aspeed-g6-pwm-tacho driver to further changes of the
pwm core outlined in the commit introducing devm_pwmchip_alloc(). There
is no intended semantical change and the driver should behave as before.

Acked-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/e95e41eea5a138ae206c9116ba3cb1d9e0178284.1710777536.git.u.kleine-koenig@pengutronix.de


Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>