MAINTAINERS: adjust for UAPI

Several headers were moved or split to uapi/.

Signed-off-by: Cesar Eduardo Barros <cesarb@cesarb.net>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>