MAINTAINERS: move Murali Karicheri to credits

His email bounces with permanent error "550 Invalid recipient". His last
email was from 2020-09-09 on the LKML and he seems to have left TI.

Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: David S. Miller <davem@davemloft.net>