ASoC: sun8i-codec: Invert Master / Slave condition

The current code had the condition backward when checking if the codec
should be running in slave or master mode.

Fix it, and make the comment a bit more readable.

Fixes: 36c68493 ("ASoC: Add sun8i digital audio codec")
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: <stable@vger.kernel.org>