net/mlx4: fix spelling mistake: "enforcment" -> "enforcement"

Trivial fix to spelling mistake in mlx4_dbg debug message

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>