ASoC: imx-pcm-rpmsg: Fix warning of incorrect type in assignment

ASoC: imx-pcm-rpmsg: Fix warning of incorrect type in assignment

The format in rpmsg is defained as unsigned char, there is warning
when convert snd_pcm_format_t to it.

sound/soc/fsl/imx-pcm-rpmsg.c:164:43: sparse: warning: incorrect type in assignment (different base types)
sound/soc/fsl/imx-pcm-rpmsg.c:164:43: sparse:    expected unsigned char format
sound/soc/fsl/imx-pcm-rpmsg.c:164:43: sparse:    got restricted snd_pcm_format_t [usertype]
sound/soc/fsl/imx-pcm-rpmsg.c:167:43: sparse: warning: incorrect type in assignment (different base types)
sound/soc/fsl/imx-pcm-rpmsg.c:167:43: sparse:    expected unsigned char format
sound/soc/fsl/imx-pcm-rpmsg.c:167:43: sparse:    got restricted snd_pcm_format_t [usertype]

Refine the unused RPMSG_DSD_U16_LE and RPMSG_DSD_U32_LE for these
case to fix this sparse warning.

Fixes: 3c00eceb2a53 ("ASoC: imx-pcm-rpmsg: Add platform driver for audio base on rpmsg")
Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Link: https://lore.kernel.org/r/1620268240-1005-1-git-send-email-shengjiu.wang@nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>