net: mscc: ocelot: fix error code in mscc_ocelot_probe()

Probe should return an error code if platform_get_irq_byname() fails
but it returns success instead.

Fixes: 6c30384e

 ("net: mscc: ocelot: register devlink ports")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/YBkXyFIl4V9hgxYM@mwanda
Signed-off-by: Jakub Kicinski <kuba@kernel.org>