net: mdiobus: fwnode_mdiobus_register_phy() rework error handling

[ Upstream commit cfaa202a ]

Rework error handling as preparation for PSE patch. This patch should
make it easier to extend this function.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 165df241 ("net: mdiobus: fix double put fwnode in the error path")
Signed-off-by: Sasha Levin <sashal@kernel.org>