s390/qeth: don't dump control cmd twice

A few lines down, qeth_prepare_control_data() makes further changes to
the control cmd buffer, and then also writes a trace entry for it.
So the first entry just pollutes the trace file with intermediate data,
drop it.

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