Remove unused variable 'dai' to eliminate below warning.

  CC      sound/soc/nuc900/nuc900-pcm.o
sound/soc/nuc900/nuc900-pcm.c: In function 'nuc900_dma_new':
sound/soc/nuc900/nuc900-pcm.c:321: warning: unused variable 'dai'
Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>