qobject: Catch another straggler for use of qdict_put_str()

Dan's addition of key-secret improvements in commit 29cf9336 was
developed prior to the addition of QDict scalar insertion macros,
but merged after the general cleanup in commit 46f5ac20.
Patch created mechanically by rerunning:
  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>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-Id: <20170624181008.25497-2-eblake@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

qemu-img.c

@@ -355,7 +355,7 @@ static int img_add_key_secrets(void *opaque,
     QDict *options = opaque;
 
     if (g_str_has_suffix(name, "key-secret")) {
-        qdict_put(options, name, qstring_from_str(value));
+        qdict_put_str(options, name, value);
     }
 
     return 0;