i40e: fix function kernel doc description

The commit c7d05ca89f8e ("i40e: driver ethtool core") introduced the
new function i40e_add_del_fdir_sctpv4() with the kernel doc
description a little bit off. The trivial error was copied over to a
different file by the commit 17a73f6b1401 ("i40e: Flow Director
sideband accounting") most recently. Fix the kernel doc with the
correct description for clarity.

Cc: Jesse Brandeburg <jesse.brandeburg@intel.com>
Cc: Joseph Gasparakis <joseph.gasparakis@intel.com>
Signed-off-by: Jean Sacren <sakiwit@gmail.com>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e_txrx.c

@@ -299,7 +299,7 @@ static int i40e_add_del_fdir_tcpv4(struct i40e_vsi *vsi,
  * @raw_packet: the pre-allocated packet buffer for FDir
  * @add: true adds a filter, false removes it
  *
- * Returns 0 if the filters were successfully added or removed
+ * Always returns -EOPNOTSUPP
  **/
 static int i40e_add_del_fdir_sctpv4(struct i40e_vsi *vsi,
 				    struct i40e_fdir_filter *fd_data,