arm: dts: mt7623: use - instead of _ in DT node name

It should be good that no use "_" is in DT node name. Consequently,
those nodes in certain files which have an inappropriate name containing
"_" are all being replaced with "-".

Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: devicetree@vger.kernel.org
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>