ASoC: fsl_asrc_dma: get codec or cpu dai from backend

With audio graph card, original cpu dai is changed to codec device in
backend, so if cpu dai is dummy device in backend, get the codec dai
device, which is the real hardware device connected.

The specific case is ASRC->SAI->AMIX->CODEC.

Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Link: https://patch.msgid.link/20250319033504.2898605-1-shengjiu.wang@nxp.com


Signed-off-by: Mark Brown <broonie@kernel.org>