net/mlx5: HWS, fixed double free in error flow of definer layout

Fix error flow bug that could lead to double free of a buffer
during a failure to calculate a suitable definer layout.

Fixes: 74a778b4 ("net/mlx5: HWS, added definers handling")
Signed-off-by: Yevgeny Kliteynik <kliteyn@nvidia.com>
Reviewed-by: Itamar Gozlan <igozlan@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>