hwmon: (oxp-sensors) Fix pwm reading

PWM reading is only 1 register long.

Signed-off-by: Joaquín Ignacio Aramendía <samsagax@gmail.com>
Link: https://lore.kernel.org/r/20221128185206.212022-1-samsagax@gmail.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>