qemu-img: Avoid qerror_report_err() outside QMP command handlers

qerror_report_err() is a transitional interface to help with
converting existing monitor commands to QMP.  It should not be used
elsewhere.  Replace by error_report_err().
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>

qemu-img.c

@@ -889,8 +889,7 @@ done:
     blk_unref(blk);
 
     if (local_err) {
-        qerror_report_err(local_err);
-        error_free(local_err);
+        error_report_err(local_err);
         return 1;
     }