gdbserver: correct log message in v_command handler (#1839)

Author: DavidLesnjak

pyocd/gdbserver/gdbserver.py

@@ -964,7 +964,7 @@ def v_command(self, client, data):
             LOG.debug("Command: vStopped notification")
             return self.create_rsp_packet(b"OK")
 
-        LOG.debug("Command: %s: Unknown command", to_str_safe(cmd))
+        LOG.debug("Command: v%s: Unknown command", to_str_safe(cmd))
         return self.create_rsp_packet(b"")
 
     # Example: $vCont;s:1;c#c1