ixgbe: fix bug in not clearing counters for X550 devices

This check was missed in when this new MAC type was added.  Since
these counts can be incremented for X550 we need to clear them.

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>