mlxsw: spectrum: Do not try to create non-existing ports during unsplit

mlxsw: spectrum: Do not try to create non-existing ports during unsplit

On some systems, when we unsplit a port we need to re-create two ports
instead. On other systems, only one needs to be re-created.

Do not try to create a port if during driver initialization it was
assigned a negative module number, which is invalid.

This avoids the following error during unsplit:
[  941.012478] mlxsw_spectrum 0000:01:00.0: Port 43: Failed to map module

The error is harmless and caused by the fact that a local port is
already mapped to module 0.

Fixes: b12b25aa18ad ("mlxsw: spectrum: Make split flow match firmware requirements")
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Arkadi Sharshevsky <arkadis@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>