ASoC: rsnd: return -EIO if rsnd_dmaen_request_channel() failed

ASoC: rsnd: return -EIO if rsnd_dmaen_request_channel() failed

PTR_ERR(NULL) is success. Normally when a function returns both NULL
and error pointers, it means that NULL is not a error.
But, rsnd_dmaen_request_channel() returns NULL if requested resource
was failed.
Let's return -EIO if rsnd_dmaen_request_channel() was failed on
rsnd_dmaen_nolock_start().
This patch fixes commit edce5c496c6a ("ASoC: rsnd: Request/Release DMA
channel eachtime")

Reported-by: Dan Carpenter <[email protected]>
Signed-off-by: Kuninori Morimoto <[email protected]>
Signed-off-by: Mark Brown <[email protected]>