MAINTAINERS: add Mike Rapoport as maintainer for userfaultfd

Link: https://lkml.kernel.org/r/20251125132908.847055-1-rppt@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Peter Xu <peterx@redhat.com>
Acked-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>