USB: adutux: Add waiting in transfer abortion

Add waiting for an URB transmit finish that let the last URB to be sent
(to be not discarded) during 'release' procedure. W/o this waiting,the
last frame will be nearly always lost.

A test case: an attempt of sending a single frame:
echo -en "\001mk255" >/dev/adutux0

Signed-off-by: Kirill Kapranov <kirill.kirillovich.kapranov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>