ASoC: soc-core: save ID if param was set in fmt_single_name()

fmt_single_name() requests "ind *id" and not allow NULL for it.
But sometimes we don't need it. Allow NULL.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://patch.msgid.link/878qm8uunz.wl-kuninori.morimoto.gx@renesas.com


Signed-off-by: Mark Brown <broonie@kernel.org>