ixgbevf: Fix kernel-doc format warnings

Recent checks added for formatting kernel-doc comments are causing warnings
if W= is run with a non-zero value.  This patch fixes function comments to
resolve warnings when W=1 is used.

Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>