net/mlx5e: fix spelling mistake: "loobpack" -> "loopback"

Trivial fix to spelling mistake in netdev_err error message
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx5/core/en_selftest.c

@@ -290,7 +290,7 @@ static int mlx5e_test_loopback(struct mlx5e_priv *priv)
 
 	if (!test_bit(MLX5E_STATE_OPENED, &priv->state)) {
 		netdev_err(priv->netdev,
-			   "\tCan't perform loobpack test while device is down\n");
+			   "\tCan't perform loopback test while device is down\n");
 		return -ENODEV;
 	}