ixgbe: list X553 backplane speeds correctly

We forgot to indicate some of the supported speed on the X553
backplane.  This patch attempts to correct for that.

Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Tested-by: Krishneil Singh <krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>