usb: common: usb-conn-gpio: use usb_role_string() to print role status

Use usb_role_string() to print role status, make the log readable.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/1621932786-9335-2-git-send-email-chunfeng.yun@mediatek.com


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