net/mlx5e: Fix error codes in alloc_branch_attr()

Set the error code if set_branch_dest_ft() fails.

Fixes: ccbe3300 ("net/mlx5e: TC, Don't offload post action rule if not supported")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>