ASoC: rsnd: fixup index of src/dst mod when capture

Index of dma name should use -1, not +1 when capture case.
Thank you Dan.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@linaro.org>