net/mlx5e: fix another maybe-uninitialized false-positive

In commit abeffce9 ("net/mlx5e: Fix a -Wmaybe-uninitialized warning"), I fixed a
gcc warning for the ipv4 offload handling. Now we get the same warning for the
added ipv6 support:

drivers/net/ethernet/mellanox/mlx5/core/en_tc.c:815:40: warning: 'out_dev' may be used uninitialized in this function [-Wmaybe-uninitialized]

We can apply the same workaround here as well.

Fixes: ce99f6b9 ("net/mlx5e: Support SRIOV TC encapsulation offloads for IPv6 tunnels")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>