Without this change, modprobe -r sfc hits the BUG_ON() in
efx_pci_remove_main().

Fixes: e7fef9b4 ("sfc: add sysfs entry to control MCDI tracing")
Reported-by: NJarod Wilson <jarod@redhat.com>
Reviewed-by: NJarod Wilson <jarod@redhat.com>
Signed-off-by: NEdward Cree <ecree@solarflare.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>