soc: mediatek: refine code to use mtk_mmsys_update_bits API

soc: mediatek: refine code to use mtk_mmsys_update_bits API

Simplify code for update  mmsys reg.

Signed-off-by: Nancy.Lin <nancy.lin@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Tested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: Bo-Chen Chen <rex-bc.chen@mediatek.com>
Reviewed-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Link: https://lore.kernel.org/r/20230113104434.28023-6-nancy.lin@mediatek.com
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>