ASoC: fsl: Fix of-node refcount unbalance in fsl_ssi_probe_from_dt()

The node obtained from of_find_node_by_path() has to be unreferenced
after the use, but we forgot it for the root node.

Fixes: f0fba2ad

 ("ASoC: multi-component - ASoC Multi-Component Support")
Cc: Timur Tabi <timur@kernel.org>
Cc: Nicolin Chen <nicoleotsuka@gmail.com>
Cc: Xiubo Li <Xiubo.Lee@gmail.com>
Cc: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Acked-by: Nicolin Chen <nicoleotsuka@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>