We forgot to unreference the platform node object obtained from
of_get_child_by_name().  This leads to the unbalance of node
refcount.

Fixes: e0ae225b ("ASoC: simple-card: support platform in dts parse")
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Acked-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>