ixgbe: cleanup redundant default method set_rxpba

My original patch 6a14ee0c "ixgbe: Add X550 support function pointers"
accidental set a default value for this structure member twice.

Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>