Include qapi/qmp/qerror.h exactly where needed

In particular, don't include it into headers.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Luiz Capitulino <lcapitulino@redhat.com>
diff --git a/balloon.c b/balloon.c
index 5f5202c..617187a 100644
--- a/balloon.c
+++ b/balloon.c
@@ -30,6 +30,7 @@
 #include "sysemu/balloon.h"
 #include "trace.h"
 #include "qmp-commands.h"
+#include "qapi/qmp/qerror.h"
 #include "qapi/qmp/qjson.h"
 
 static QEMUBalloonEvent *balloon_event_fn;