pwm: atmel-hlcdc: Use pwmchip_add() instead of pwmchip_add_with_polarity()

The only side effect of this change is that pwm->state.polarity is
initialized to PWM_POLARITY_NORMAL instead of PWM_POLARITY_INVERSED.
However all other members of pwm->state are uninitialized and consumers
are expected to provide the right polarity (either by setting it explicitly
or by using a helper like pwm_init_state() that overwrites .polarity
anyhow with a value independent of the initial value).

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