ASoC: soc.h: return error if multi platform at snd_soc_fixup_dai_links_platform_name()

snd_soc_fixup_dai_links_platform_name() is assuming it is single platform.
return error if multi platforms.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/871rc7aoo9.wl-kuninori.morimoto.gx@renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>