arm64: dts: mt8173: fix wrong power-domain phandle of pmic

arm64: dts: mt8173: fix wrong power-domain phandle of pmic

Due to power domain controller is added, the power domain's
phanle is also changed from 'scpsys' to 'spm', but forget to
modify pmic node's

Fixes: 8b6562644df9 ("arm64: dts: mediatek: Add mt8173 power domain controller")
Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Reviewed-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Link: https://lore.kernel.org/r/1616048328-13579-1-git-send-email-chunfeng.yun@mediatek.com
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>