qobject: Update coccinelle script to catch Q{INC, DEC}REF

The recent commit b097efc0 used qobject_decref(QOBJECT(E)), even
though we already have QDECREF(E) for that purpose.  We can update
our coccinelle script to catch any future relapses; with that in
place, the rest of the patch is generated with:
 spatch --sp-file scripts/coccinelle/qobject.cocci \
        --macro-file scripts/cocci-macro-file.h --dir . --in-place

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20170624181008.25497-3-eblake@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>