usb: phy-ulpi-viewport: convert to readl_poll_timeout_atomic()

Use readl_poll_timeout_atomic() to simplify code

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/1600668815-12135-8-git-send-email-chunfeng.yun@mediatek.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>