MAINTAINERS: adjust for UAPI

Several headers were moved or split to uapi/.
Signed-off-by: NCesar Eduardo Barros <cesarb@cesarb.net>
Acked-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>