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/block.c b/block.c
index b07f987..e2e33fd 100644
--- a/block.c
+++ b/block.c
@@ -28,6 +28,7 @@
 #include "block/blockjob.h"
 #include "qemu/error-report.h"
 #include "qemu/module.h"
+#include "qapi/qmp/qerror.h"
 #include "qapi/qmp/qjson.h"
 #include "sysemu/block-backend.h"
 #include "sysemu/sysemu.h"