qemu: getAutoDumpPath() return value should be dumpfile not domname.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1354238

So we spend some time and effort constructing perfect file name
for an automatic coredump of a domain, but then just leak it and
use the domain name anyway. This is probably due to a silly
mistake that slipped even through review.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

src/qemu/qemu_driver.c

@@ -3869,7 +3869,8 @@ getAutoDumpPath(virQEMUDriverPtr driver,
                              timestr));
 
     virObjectUnref(cfg);
-    return domname;
+    VIR_FREE(domname);
+    return dumpfile;
 }
 
 static void