ASoC: Intel: cht: fix uninit variable warning

Kbuild bot reports that we might use dai_index uninitialized.

sound/soc/intel/boards/cht_bsw_rt5645.c:391:37: warning: 'dai_index' may be used uninitialized in this function [-Wmaybe-uninitialized]

Since it is theoretically possible, set it while initializing.

Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>