ixgbe: Resolve null function pointer accesses on 82598 w/ multi-speed fiber

This change resolves some null function pointer accesses on 82598 when a
multi-speed fiber module is inserted into the adapter.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Ross Brattain <ross.b.brattain@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>