ixgbe: replace reference to CONFIG_FCOE with IXGBE_FCOE

CONFIG_FCOE is not the correct define to check since it is possible for it
to be CONFIG_FCOE_MODULE, as such the reference to it should be replaced
with IXGBE_FCOE.

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>