net: mscc: ocelot: allow probing to continue with ports that fail to register

The existing ocelot device trees, like ocelot_pcb123.dts for example,
have SERDES ports (ports 4 and higher) that do not have status = "disabled";
but on the other hand do not have a phy-handle or a fixed-link either.

So from the perspective of phylink, they have broken DT bindings.

Since the blamed commit, probing for the entire switch will fail when
such a device tree binding is encountered on a port. There used to be
this piece of code which skipped ports without a phy-handle:

	phy_node = of_parse_phandle(portnp, "phy-handle", 0);
	if (!phy_node)
		continue;

but now it is gone.

Anyway, fixed-link setups are a thing which should work out of the box
with phylink, so it would not be in the best interest of the driver to
add that check back.

Instead, let's look at what other drivers do. Since commit 86f8b1c0
("net: dsa: Do not make user port errors fatal"), DSA continues after a
switch port fails to register, and works only with the ports that
succeeded.

We can achieve the same behavior in ocelot by unregistering the devlink
port for ports where ocelot_port_phylink_create() failed (called via
ocelot_probe_port), and clear the bit in devlink_ports_registered for
that port. This will make the next iteration reconsider the port that
failed to probe as an unused port, and re-register a devlink port of
type UNUSED for it. No other cleanup should need to be performed, since
ocelot_probe_port() should be self-contained when it fails.

Fixes: e6e12df6

 ("net: mscc: ocelot: convert to phylink")
Reported-and-tested-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>