pwm: gpio: Switch to use hrtimer_setup()

hrtimer_setup() takes the callback function pointer as argument and
initializes the timer completely.

Replace hrtimer_init() and the open coded initialization of
hrtimer::function with the new setup mechanism.

Acked-by: Zack Rusin <zack.rusin@broadcom.com>
Signed-off-by: Nam Cao <namcao@linutronix.de>
Link: https://lore.kernel.org/r/7b7115da84372a49e36a0ac1a5ce553129c3ce0b.1738746904.git.namcao@linutronix.de


Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>