dma: rcar-audmapp: Fix for no corresponding slave ID

In case of no corresponding slave ID, the audmapp_set_slave() returns
-ENXIO same as sh_dmae_set_slave() of shdmac.c.
DMAEngine might return wrong channel without this patch

Signed-off-by: Ryo Kataoka <ryo.kataoka.wt@renesas.com>
Signed-off-by: Jun Watanabe <jun.watanabe.ue@renesas.com&gt;,>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>