atl1: fix vlan tag regression

Commit 401c0aab introduced a regression
in the atl1 driver by storing the VLAN tag in the wrong TX descriptor
field.

This patch causes the VLAN tag to be stored in its proper location.

Tested-by: Ramon Casellas <ramon.casellas@cttc.es>
Signed-off-by: Jay Cliburn <jacliburn@bellsouth.net>
Cc: stable@kernel.org
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>