ASoC: rsnd: don't use prohibited number to PDMACHCRn.SRS

Current rsnd_dmapp_get_id() returns 0xFF as error code if system used
strange connection. It will be used as PDMACHCRn.SRS, but 0xFF is
prohibited number.
In order not to use prohibited number, this patch indicates error message
and returns 0x00 (same as SSI00) in error case.
Special thanks to Dung-san.

Reported-by: Nguyen Viet Dung <nv-dung@jinso.co.jp>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>