common/mlx5: use just sufficient barrier for Arm

cqe->op_own indicates if the CQE is owned by the NIC.
The rest of the fields in CQE should be read only after op_own is read.
On Arm platforms using "dmb ishld" is sufficient to enforce this.

Fixes: 88c07335 ("net/mlx5: extend Rx completion with error handling")
Cc: stable@dpdk.org

Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>