net:enetc: bug fix for qos sfi operate space after freed

'Dan Carpenter' reported:
This code frees "sfi" and then dereferences it on the next line:
>                 kfree(sfi);
>                 clear_bit(sfi->index, epsfp.psfp_sfi_bitmap);

This "sfi->index" should be "index".
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NPo Liu <Po.Liu@nxp.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/enetc/enetc_qos.c

@@ -903,7 +903,7 @@ static void stream_filter_unref(struct enetc_ndev_priv *priv, u32 index)
 		enetc_streamfilter_hw_set(priv, sfi, false);
 		hlist_del(&sfi->node);
 		kfree(sfi);
-		clear_bit(sfi->index, epsfp.psfp_sfi_bitmap);
+		clear_bit(index, epsfp.psfp_sfi_bitmap);
 	}
 }