ixgbe: fix default mac->ops.setup_link for X550EM

X550EM_a/x did not have a default value for mac->ops.setup_link which
was causing link issues for backplane devices.

This patch sets mac->ops.setup_link to ixgbe_setup_mac_link_X540 for
X550EM_a/x which is also default for X550. This will result in
mac->ops.setup_link calling the link setup function for the respective
PHY type in case we do not need a special function to deal with it.
Reported-by: Ken Cox <jkc@redhat.com>
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

@@ -2908,7 +2908,7 @@ static const struct ixgbe_mac_operations mac_ops_X550EM_x = {
 	.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,
@@ -2926,7 +2926,7 @@ 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,