qerror: Move #include out of qerror.h

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/qemu-nbd.c b/qemu-nbd.c
index 7a4bf1b..5106b80 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -25,6 +25,7 @@
 #include "qemu/error-report.h"
 #include "block/snapshot.h"
 #include "qapi/util.h"
+#include "qapi/qmp/qstring.h"
 
 #include <stdarg.h>
 #include <stdio.h>