mlxsw: spectrum_router: Avoid uninitialized symbol errors

Suppress the following smatch errors. None of these are actually
possible with current code paths.

drivers/net/ethernet/mellanox/mlxsw//spectrum_router.c:1220
mlxsw_sp_ipip_entry_find_decap() error: uninitialized symbol 'saddrp'.
drivers/net/ethernet/mellanox/mlxsw//spectrum_router.c:1220
mlxsw_sp_ipip_entry_find_decap() error: uninitialized symbol
'saddr_len'.
drivers/net/ethernet/mellanox/mlxsw//spectrum_router.c:1221
mlxsw_sp_ipip_entry_find_decap() error: uninitialized symbol
'saddr_prefix_len'.

drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:1390
mlxsw_sp_netdevice_ipip_ol_reg_event() error: uninitialized symbol
'ipipt'.

drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:3255
mlxsw_sp_nexthop_group_update() error: uninitialized symbol 'err'.

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