ASoC: Blackfin I2S: fix resume handling

There is no need to manually start playback/capture ourselves as the PCM
driver will handle things for us.

Signed-off-by: Cliff Cai <cliff.cai@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>