mlxsw: spectrum: Make VLAN deletion function symmetric

Commit 05978481 ("mlxsw: spectrum: Create PVID vPort before
registering netdevice") removed __mlxsw_sp_port_vlans_del() from the
init sequence of the driver, which forced it to be non-symmetric with
regards to __mlxsw_sp_port_vlans_add().

Make both functions symmetric as the constraint no longer exists.

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