This prepares the driver for further changes that will drop struct
pwm_chip chip from struct berlin_pwm_chip. Use the pwm_chip as driver
data instead of the berlin_pwm_chip to get access to the pwm_chip in
berlin_pwm_suspend() and berlin_pwm_resume() without using bpc->chip.

Link: https://lore.kernel.org/r/d2a0c5b664ef1bfd4719c645c069717d63fb4e65.1707900770.git.u.kleine-koenig@pengutronix.deSigned-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>