net: ethernet: ti: cpsw: fix runtime_pm while add/kill vlan

It's exclusive with normal behaviour but if try to set vlan to one of
the reserved values is made, the cpsw runtime pm is broken.

Fixes: a6c5d14f ("drivers: net: cpsw: ndev: fix accessing to suspended device")
Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>