This prepares the driver for further changes that will drop struct
pwm_chip chip from struct atmel_tcb_pwm_chip. Use the pwm_chip as driver
data instead of the atmel_tcb_pwm_chip to get access to the pwm_chip in
the .suspend() and .resume() callbacks and atmel_tcb_pwm_remove()
without using tcbpwm->chip.

Link: https://lore.kernel.org/r/6a90083e9d1ab1c34422161593d6d7a669143217.1707900770.git.u.kleine-koenig@pengutronix.deSigned-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>