gpio: mvebu/pwm: Refuse requests with inverted polarity

[ Upstream commit 3ecb10175b1f776f076553c24e2689e42953fef5 ]

The driver doesn't take struct pwm_state::polarity into account when
configuring the hardware, so refuse requests for inverted polarity.

Fixes: 757642f9 ("gpio: mvebu: Add limited PWM support")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
Signed-off-by: Sasha Levin <sashal@kernel.org>