ASoC: pcm: Refactor soc_pcm_apply_msb for multicodecs

Refactor the function to facilitate the migration to
multiple codecs.

Fix a trailing space in the header as well.

No functional change.

Signed-off-by: Benoit Cousson <bcousson@baylibre.com>
Signed-off-by: Mark Brown <broonie@linaro.org>