ixgbe: add default setup_link for x550em_a MAC type

Add default setting for mac->ops.setup_link on x550em_a MAC types.
This fixes a link issue on KR parts.

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/ixgbe/ixgbe_x550.c

@@ -3795,7 +3795,7 @@ static struct ixgbe_mac_operations mac_ops_x550em_a = {
 	.get_media_type		= ixgbe_get_media_type_X550em,
 	.get_san_mac_addr	= NULL,
 	.get_wwn_prefix		= NULL,
-	.setup_link		= NULL, /* defined later */
+	.setup_link		= &ixgbe_setup_mac_link_X540,
 	.get_link_capabilities	= ixgbe_get_link_capabilities_X550em,
 	.get_bus_info		= ixgbe_get_bus_info_X550em,
 	.setup_sfp		= ixgbe_setup_sfp_modules_X550em,