ARM: dts: imx6qdl-nitrogen6_som2: fix rv4162 compatible

The rv4162 vendor is microcrystal, not ST.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Gary Bisson <gary.bisson@boundarydevices.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>