pwm: sun4i: Prepare removing pwm_chip from driver data

pwm: sun4i: Prepare removing pwm_chip from driver data

This prepares the driver for further changes that will drop struct
pwm_chip chip from struct sun4i_pwm_chip. Use the pwm_chip as driver
data instead of the sun4i_pwm_chip to get access to the pwm_chip in
sun4i_pwm_remove() without using sun4ichip->chip.

Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Link: https://lore.kernel.org/r/f8e3fb96fe341ba0a4bed982aa731c5c7c355b83.1707900770.git.u.kleine-koenig@pengutronix.de
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>