usb: mtu3: skip getting extcon when use manual drd switch

When use manual drd switch, extcon is not used in fact, so no
need get it even it exists, just skip it like using role switch.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/1622182260-23767-5-git-send-email-chunfeng.yun@mediatek.com


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