pwm: dwc: Prepare removing pwm_chip from driver data

pwm: dwc: Prepare removing pwm_chip from driver data

This prepares the driver for further changes that will drop struct
pwm_chip chip from struct dwc_pwm. Use the pwm_chip as driver
data and return value of dwc_pwm_alloc() instead of the dwc_pwm to get
access to the pwm_chip in dwc_pwm_probe() and dwc_pwm_suspend() without
using dwc->chip.

Thanks to Raag Jadav for providing a hunk of this patch that Uwe missed
during creation of this patch.

Link: https://lore.kernel.org/r/008ce5ab84b8e3baa3e81ab6d36dbb0e4be5c319.1707900770.git.u.kleine-koenig@pengutronix.de
Link: https://lore.kernel.org/r/20240219033835.11369-2-raag.jadav@intel.com
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>