ARM: dts: imx6qdl-vicut1.dtsi: Fix node name backlight_led

This naming error slipped through, so now that a new backlight node has
been added with correct spelling, fix this one also.

Fixes: 98efa526 ("ARM: dts: imx6qdl-vicut1/vicutgo: Add backlight_led node")
Signed-off-by: David Jander <david@protonic.nl>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>