pwm: meson: Simplify duplicated per-channel tracking

[ Upstream commit 5f97f18feac9bd5a8163b108aee52d783114b36f ]

The driver tracks per-channel data via struct pwm_device::chip_data and
struct meson_pwm::channels[]. The latter holds the actual data, the former
is only a pointer to the latter. So simplify by using struct
meson_pwm::channels[] consistently.

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>
Stable-dep-of: 87a2cbf02d77 ("pwm: meson: fix handling of period/duty if greater than UINT_MAX")
Signed-off-by: Sasha Levin <sashal@kernel.org>