hso: fix for the 'invalid frame length' messages

Some devices cannot send very short usb transfers. To get around this the
firmware adds a known pattern and flags the driver that it should check for
this pattern on short transfers. This flag was not taken into account by
the driver.

Signed-off-by: Jan Dumon <j.dumon@option.com>
Signed-off-by: David S. Miller <davem@davemloft.net>