rt2x00: Fix URB error handling

kill_urb guarentees that when the function returns, the URB has
been fully killed. This means we don't need the extra sleeping
after the call to kill_urb.

kill_urb can however also guarentee the submit_urb to fail, as
a result, we must catch the return value from submit_urb an
correctly mark the entry as owned by the driver, and the
status as broken.

Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>