The default of_xlate callback (of_pwm_xlate_with_flags()) does
everything the drivers expects from its .of_xlate() callback. So drop
the custom implementation.

Link: https://lore.kernel.org/r/f58336c298d536107de5cab6a57e19f957ab326c.1704835845.git.u.kleine-koenig@pengutronix.deSigned-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>