ALSA: ASoC: OMAP: Set DMA stream name at runtime in McBSP DAI driver

This suits better when adding support for multiple links and different
link formats.

Signed-off-by: Jarkko Nikula <jarkko.nikula@nokia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>