mlxsw: minimal: Fix an error handling path in 'mlxsw_m_port_create()'

An 'alloc_etherdev()' called is not ballanced by a corresponding
'free_netdev()' call in one error handling path.

Slighly reorder the error handling code to catch the missed case.

Fixes: c100e47c ("mlxsw: minimal: Add ethtool support")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>