arm64: dts: mt8173-evb: fix model name

Model name in mt8173-evb.dts doesn't follow dts convention (it should
be human readable model name). Fix it.

Fixes: b3a37248 ("arm64: dts: Add mediatek MT8173 SoC and evaluation board dts and Makefile")
Cc: <stable@vger.kernel.org> # v4.0+
Signed-off-by: Yingjoe Chen <yingjoe.chen@mediatek.com>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>