mlxsw: spectrum: Fix helper function and port variable names

Commit dd82364c

 ("mlxsw: Flip to the new dev walk API") did some
small changes in mlxsw code, but it did not respect the naming
conventions. So fix this now.

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