mlxsw: spectrum: Use mapping of port being split for creating split ports

Don't use constant max width value and instead of that, use the actual
width of the port. Also don't pass module value and use the value
stored in the same structure.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Reviewed-by: Shalom Toledo <shalomt@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>