MAINTAINERS: add an explicit entry for tm6000

MAINTAINERS: add an explicit entry for tm6000

While this file was always maintained, there was no explicit entry
for it.

There aren't many things happening at tm6000 side for a long time:
Driver works. This chip is already not sold anymore, so I don't
expect much changes on its side.

So, add a new entry with status equal to Odd fixes to better
reflect it.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>