The pwm devices for a pwm_chip are numbered starting at 0, the first hw
channel however has the number 1. While introducing a parametrised macro
to simplify register bit usage and making that offset explicit, one of
the usages was converted wrongly. This is fixed here.

Fixes: 7cea05ae ("pwm-stm32: Make use of parametrised register definitions")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://lore.kernel.org/r/20240905090627.197536-2-u.kleine-koenig@baylibre.comSigned-off-by: Uwe Kleine-König <ukleinek@kernel.org>