net: ethernet: renesas: rswitch: Fix ethernet-ports handling

If one of ports in the ethernet-ports was disabled, this driver
failed to probe all ports. So, fix it.

Fixes: 3590918b

 ("net: ethernet: renesas: Add support for "Ethernet Switch"")
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://lore.kernel.org/r/20230120001959.1059850-1-yoshihiro.shimoda.uh@renesas.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>