phy: phy-mtk-tphy: use new io helpers to access register

Use new helpers mtk_phy_clear/set/update_bits() to access registers
Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/20211218082802.5256-5-chunfeng.yun@mediatek.comSigned-off-by: Vinod Koul <vkoul@kernel.org>