MT7986's watchdog embeds a reset controller and needs only the
mediatek,mt7986-wdt compatible string as the MT6589 one is there
for watchdogs that don't have any reset controller capability.
Fixes: 50137c150f5f ("arm64: dts: mediatek: add basic mt7986 support")
Signed-off-by: Allen-KH Cheng <allen-kh.cheng@xxxxxxxxxxxx>