pwm: hibvt: Explicitly set .polarity in .get_state()

The driver only both polarities. Complete the implementation of
.get_state() by setting .polarity according to the configured hardware
state.

Fixes: d09f0081

 ("pwm: Add PWM driver for HiSilicon BVT SOCs")
Link: https://lore.kernel.org/r/20230228135508.1798428-2-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>