arm64: dts: mt8173: change node name

- Change the node name from "mt6397" to "pmic" to be consistent
with the generic names recommendation.

Signed-off-by: Alexandre Mergnat <amergnat@baylibre.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20221005-mt6357-support-v8-5-560caaafee53@baylibre.com


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>