net/mlx5: E-Switch, Fix error flow in the SRIOV e-switch init code

When enablement of the SRIOV e-switch in certain mode (switchdev or legacy)
fails, we must set the mode to none. Otherwise, we'll run into double free
based crashes when further attempting to deal with the e-switch (such
as when disabling sriov or unloading the driver).

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>