ASoC: sun4i-i2s: Switch to devm for PCM register

Since the introduction of the driver, a new managed helper for the
dmaengine PCM registration has been created. Let's use it to simplify a bit
our probe and remove functions.

Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://lore.kernel.org/r/606d271187091e858e8c15e20555af0b79798fe1.1566242458.git-series.maxime.ripard@bootlin.com


Signed-off-by: Mark Brown <broonie@kernel.org>