ixgbe: fix X550 PHY function pointers

ixgbe: fix X550 PHY function pointers

Orabug: 21669416

A subset of the X550 function pointers didn't have default methods. This
didn't cause any issue with previous X550 devices as they were all
redefined.  However future devices will need these default values.

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>
(cherry picked from commit bef23de1e57654e9c05be3e428b9158908a327bb)
Signed-off-by: Brian Maly <brian.maly@oracle.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>