rtl8xxxu: prevent leaking urb

In rtl8xxxu_submit_int_urb if usb_submit_urb fails the allocated urb
should be released.

Signed-off-by: Navid Emamdoost <navid.emamdoost@gmail.com>
Reviewed-by: Chris Chiu <chiu@endlessm.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
