s390/qeth: don't convert return code twice

qeth_l2_send_groupmac() already translates the return code, so
calling qeth_setdel_makerc() a second time only produces garbage.

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