ARM: dts: imx6dl-b1x5pv2: Fix simple-audio routing property

Per simple-card.yaml, 'simple-audio-card,audio-routing' is not a valid
property.

Change it to 'simple-audio-card,routing'.

Signed-off-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>