igb: Remove dead code path

The 82575 manual initialization scripts are not supported on 82580 and
above. Rather than call the function to immediately return, clarify the
code by removing this pointless function call.

Signed-off-by: Matthew Vick <matthew.vick@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>