i40e: Fix unexpected MFS warning message

Commit 3a2c6ced ("i40e: Add a check to see if MFS is set") added
a warning message that reports unexpected size of port's MFS (max
frame size) value. This message use for the port number local
variable 'i' that is wrong.
In i40e_probe() this 'i' variable is used only to iterate VSIs
to find FDIR VSI:

<code>
...
/* if FDIR VSI was set up, start it now */
        for (i = 0; i < pf->num_alloc_vsi; i++) {
                if (pf->vsi[i] && pf->vsi[i]->type == I40E_VSI_FDIR) {
                        i40e_vsi_open(pf->vsi[i]);
                        break;
                }
        }
...
</code>

So the warning message use for the port number index of FDIR VSI
if this exists or pf->num_alloc_vsi if not.

Fix the message by using 'pf->hw.port' for the port number.

Fixes: 3a2c6ced

 ("i40e: Add a check to see if MFS is set")
Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>