arm64: dts: imx8mq-librem5-devkit: Don't use underscore in node name

Rename usb_typec to usb-typec to get a rid of a warning when building
dtb with warnings enabled.

Signed-off-by: Guido Günther <agx@sigxcpu.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>