net/mlx5e: Fix a use after free on error in mlx5_tc_ct_shared_counter_get()

This code frees "shared_counter" and then dereferences on the next line
to get the error code.

Fixes: 1edae233 ("net/mlx5e: CT: Use the same counter for both directions")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>