net/mlx4_core: A write memory barrier is sufficient in EQ ci update

Soften the memory barrier call of mb() by a sufficient wmb() in the
consumer index update of the event queues.
Suggested-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NTariq Toukan <tariqt@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx4/eq.c

@@ -100,7 +100,7 @@ static void eq_set_ci(struct mlx4_eq *eq, int req_not)
 					       req_not << 31),
 		     eq->doorbell);
 	/* We still want ordering, just not swabbing, so add a barrier */
-	mb();
+	wmb();
 }
 
 static struct mlx4_eqe *get_eqe(struct mlx4_eq *eq, u32 entry, u8 eqe_factor,