netxen_nic: Remove unused pointer hdr in netxen_setup_minidump()

Pointer hdr in netxen_setup_minidump() is set but never used, thus
should be removed.

Signed-off-by: Christos Gkekas <chris.gekas@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>