ASoC: sun4i-i2s: Check for slave select bit

The newer SoCs do not have this setting. Instead they set the pin
direction. Add a check to see if the bit is valid and if so set
it accordingly.

Signed-off-by: Marcus Cooper <codekipper@gmail.com>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Mark Brown <broonie@kernel.org>