RDMA/mlx5: Init dest_type when create flow

When using action drop dest_type was never assigned to any value.  Add
initialization of dest_type to -1 since 0 is valid.

Fixes: f29de9ee ("RDMA/mlx5: Add support for drop action in DV steering")
Link: https://lore.kernel.org/r/20200707110259.882276-1-leon@kernel.org


Signed-off-by: Daria Velikovsky <daria@mellanox.com>
Reviewed-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>