pwm: Return -EINVAL for old-style drivers without .set_polarity callback

Since commit 2b1c1a5d ("pwm: Use -EINVAL for unsupported polarity")
all drivers implementing the apply callback are unified to return
-EINVAL if an unsupported polarity is requested. Do the same in the
compat code for old-style drivers.

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