pwm: meson: Drop useless check for channel data being NULL

In meson_pwm_free() the function pwm_get_chip_data() always returns a
non-NULL pointer because it's only called when the request callback
succeeded and this callback calls pwm_set_chip_data() in this case.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>