net/mlx5e: Fix memory leak on updating vport counters

When updating statistics driver queries the vport's counters. On fail,
add error path releasing the allocated buffer avoiding memory leak.

Fixes: 64b68e36

 ("net/mlx5: Refactor and expand rep vport stat group")
Signed-off-by: Aya Levin <ayal@nvidia.com>
Reviewed-by: Maor Dickman <maord@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>