pwm: Mention PWM chip ID in /sys/kernel/debug/pwm

While it's not hard to match the entries from /sys/kernel/debug/pwm to
the corresponding pwmchip in /sys/class/pwm, it's a bit simpler to have
the number mentioned in /sys/kernel/debug/pwm.

Link: https://lore.kernel.org/r/20230808165250.942396-3-u.kleine-koenig@pengutronix.de


Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>