usb: mtu3: return successful suspend status

Forgot 'return 0;' when suspend successfully, make the mistake
when I split patches.

Fixes: 6b587394 ("usb: mtu3: support suspend/resume for dual-role mode")
Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/20210826083637.33237-1-chunfeng.yun@mediatek.com


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