Documentation: Fix typo in devlink documentation

The driver is named "mlxsw", not "mlx5".

Fixes: d4255d75 ("devlink: document info versions for each driver")
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>