arm: dts: mt7623: fix the regulators mmc should use on bananapi-r2

Both mmc devices on bananapi-r2 board should all use the fixed regulators
as their power source instead of PMIC MT6323 exports.

Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>