s390/qeth: remove unused parameter

'elements_needed' is not used in qeth_do_send_packet_fast(),
so consequently remove it.

Signed-off-by: Julian Wiedmann <jwi@linux.vnet.ibm.com>
Acked-by: Ursula Braun <ubraun@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>