MAINTAINERS: Fix Max's and Shravan's emails

Max's and Shravan's usernames were changed while @mellanox.com emails
were transferred to be @nvidia.com.

Fixes: f6da70d9 ("MAINTAINERS: Update Mellanox and Cumulus Network addresses to new domain")
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>