net: ethernet: renesas: rswitch: Fix error path in renesas_eth_sw_probe()

If rswitch_init() returns non-zero and this driver is re-probed,
the following error happens:

    renesas_eth_sw e6880000.ethernet: Unbalanced pm_runtime_enable!

So, fix error path in renesas_eth_sw_probe().

Fixes: 3590918b ("net: ethernet: renesas: Add support for "Ethernet Switch"")
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>