pwm: sti: Fix capture for st,pwm-num-chan < st,capture-num-chan

The driver only used the number of pwm channels to set the pwm_chip's
npwm member. The result is that if there are more capture channels than
PWM channels specified in the device tree, only a part of the capture
channel is usable. Fix that by passing the bigger channel count to the
pwm framework. This makes it possible that the .apply() callback is
called with .hwpwm >= pwm_num_devs, catch that case and return an error
code.

Fixes: c97267ae

 ("pwm: sti: Add PWM capture callback")
Link: https://lore.kernel.org/r/20240204212043.2951852-2-u.kleine-koenig@pengutronix.de
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>