usb: dwc3: drd: use helper to get role-switch-default-mode

Use the new helper usb_get_role_switch_default_mode() to
get property of "role-switch-default-mode"

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/1626340078-29111-7-git-send-email-chunfeng.yun@mediatek.com


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