ASoC: rsnd: check src mod pointer for rsnd_mod_id()

Without this patch, gcc 4.9.x says

    sound/soc/sh/rcar/cmd.c: In function 'rsnd_cmd_init':
    sound/soc/sh/rcar/cmd.c:85:14: warning: array subscript is below array\
	bounds [-Warray-bounds]
	data = path[rsnd_mod_id(src)] |
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/sh/rcar/cmd.c

@@ -82,6 +82,9 @@ static int rsnd_cmd_init(struct rsnd_mod *mod,
 			[9] = 0x2,
 		};
 
+		if (unlikely(!src))
+			return -EIO;
+
 		data = path[rsnd_mod_id(src)] |
 			cmd_case[rsnd_mod_id(src)] << 16;
 	}