MAINTAINERS: Update Mellanox's mlx4 Eth NIC driver entry

Tariq Toukan is replacing Eugenia (Jenny) Emantayev as the mlx4
Ethernet driver maintainer, thanks to Jenny and good luck to him.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>