phy: phy-pxa-28nm-usb2: convert to readl_poll_timeout()

Use readl_poll_timeout() to simplify code

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/1598320987-25518-6-git-send-email-chunfeng.yun@mediatek.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>