MAINTAINERS: Update QAPI stanza for commit fb0bc835

Commit fb0bc835 moved code from scripts/qapi-*.py to
scripts/qapi/*.py.  It neglected to update MAINTAINERS: scripts/qapi*
matches only the former, not the latter.  Do that now.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20180620124827.17106-1-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>