pwm: fsl-ftm: Change prototype of a helper to prepare further changes

This prepares the driver for further changes that will make it harder to
determine the pwm_chip from a given fsl_pwm_chip. To just not have to
do that, rework fsl_pwm_apply_config() to take a pwm_chip.

Link: https://lore.kernel.org/r/5f0e88afe25d6a218032891a34f963980814b760.1707900770.git.u.kleine-koenig@pengutronix.de


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