[CIFS] Fix endian conversion of vcnum field

When multiply mounting from the same client to the same server, with
different userids, we create a vcnum which should be unique if
possible (this is not the same as the smb uid, which is the handle
to the security context).  We were not endian converting additional
(beyond the first which is zero) vcnum properly.

CC: Stable <stable@kernel.org>
Acked-by: Shirish Pargaonkar <shirishp@us.ibm.com>
Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>