arm64: dts: mediatek: mt8188: Fix wrong clock provider in MFG1 power domain

arm64: dts: mediatek: mt8188: Fix wrong clock provider in MFG1 power domain

The clock index "CLK_APMIXED_MFGPLL" belongs to the "apmixedsys" provider,
so fix the index.

In addition, add a "mfg1" label so following commits could set
domain-supply for MFG1 power domain.

Fixes: eaf73e4224a3 ("arm64: dts: mediatek: mt8188: Add support for SoC power domains")
Signed-off-by: Pablo Sun <pablo.sun@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20241002022138.29241-2-pablo.sun@mediatek.com
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>