i40e: fix function kernel doc description

The commit c7d05ca8 ("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 17a73f6b ("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>