ASoC: rsnd: don't call unneeded of_node_put() on dma.c

Current rsnd_dmaen_start() is calling of_node_put() for np,
but it is not needed if it goes through this loop.
This patch tidyup it

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>