MLK-15043-2: ASoC: imx-cs42888: fix noise issue with FE-BE case

MLK-15043-2: ASoC: imx-cs42888: fix noise issue with FE-BE case

The case is "aplay -Dhw:0,1 -d 5 -r 8000 -f S16_LE -c 9 audio8k16b9c.wav",
which is to playback 9 channel bitstream. But the maximum supported channel
of codec is 8, ALSA didn't return error for this case, but continue to
playback.

The reason is that in FE-BE case, ASLA only get the FE's hw parameter for
constraint list, omit the BE's parameter. This patch is to merge BE's
parameter to FE. in this situation with the 9 channel case, ASLA will
return error "aplay: set_params:1303: Channels count non available"

Signed-off-by: Shengjiu Wang <shengjiu.wang@freescale.com>
(cherry picked from commit cfe36e2e7fce578eeac9a36eac04db2584e6e92e)