MAINTAINERS: Add myself as maintainer of ehv_bytechan tty driver

Michael Ellerman made a call for volunteers from NXP to maintain
this driver and I offered myself.

Signed-off-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Acked-by: Timur Tabi <timur@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200114110012.17351-1-laurentiu.tudor@nxp.com