MAINTAINERS: update maintainer list for AMD NTB driver

updating with my email address.

Signed-off-by: Sanjay R Mehta <sanju.mehta@amd.com>
Signed-off-by: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>