xtensa/esp32: set cpuint to initial value after deallocate

on ESP32, cpuint was allocated when register wdt handler, but not
deallocated when unregister, which cause debug assert when checking
`DEBUGASSERT((*freeints & bitmask) == 0)`, so set cpuint to initial value
after deallocate.

The same issue on ESP32s3 has been fixed by PR#15433

arch/xtensa/src/esp32/esp32_wdt.c

@@ -733,6 +733,7 @@ static int esp32_wdt_setisr(struct esp32_wdt_dev_s *dev, xcpt_t handler,
               up_disable_irq(wdt->irq);
               esp32_teardown_irq(wdt->cpu, wdt->periph, wdt->cpuint);
               irq_detach(wdt->irq);
+              wdt->cpuint = -ENOMEM;
             }
 
           goto errout;