igb: Remove unneeded FIXME

Remove a FIXME comment that was missed in a commit on 1/2007.

Signed-off-by: Todd Fujinaka <todd.fujinaka@intel.com>
Reported-by: nick <xerofoify@gmail.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>