net/mlx5: fix unreachable MPLS error path

net/mlx5: fix unreachable MPLS error path

The mlx5_flow_validate_item_mpls function checks MPLS item validation.
It first checks if the device supports MPLS, it is done using the ifdef
condition that if it fails to skip to endif and return the appropriate
error.

When MPLS is supported, the preprocessor will copy the body of the
function ending with return 0 followed by the lines that report MPLS
support.
In fact, these lines are unreachable because before them the function
returns 0 and in any case they are unnecessary.

Replace the endif by else and move endif to the end of the
function.

Fixes: 23c1d42c7138 ("net/mlx5: split flow validation to dedicated function")
Cc: stable@dpdk.org
Signed-off-by: Michael Baum <michaelba@mellanox.com>
Acked-by: Matan Azrad <matan@mellanox.com>