net/mlx5e: Simplify get_route_and_out_devs helper function

The helper function has "if" branches that do the same. Merge them to
simplify the code.

Signed-off-by: Eli Britstein <elibr@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>