ASoC: tlv320aic3x: Fix slot width for non tdm mode playback

For machines using tlv320aic3x for dsp based decoding of compressed
audio there is no substream structure available. If tlv320aic3x is
used in I2S mode the slot width is supposed to be equal to bit width.
However if machine supports compressed audio decode using dsp the
structure will be cstream instead of substream. this will result in
invalid access. Avoid invalid access to substream structure by setting
slot_width with bit width in hw_param.

Change-Id: I95c83aba8f6144d1659eaeb927e6bae09fd9aa09
Signed-off-by: Asish Bhattacharya <asishb@codeaurora.org>