ASoC: fix W=1 build warnings

We get 1 warning about global functions without a declaration
in the ASoC sub-system when building with W=1:

sound/soc/sh/rcar/core.c:113:6: warning: no previous prototype for 'rsnd_mod_make_sure' [-Wmissing-prototypes]
 void rsnd_mod_make_sure(struct rsnd_mod *mod, enum rsnd_mod_type type)

In this case, the function 'rsnd_mod_make_sure' is declared in rsnd.h file,
but it only valid if the macro DEBUG is claimed.

so the implementation of function 'rsnd_mod_make_sure' need be
held by macro DEBUG.

Signed-off-by: Baoyou Xie <baoyou.xie@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>