nrf: PWMAudioOut: deactivate PWM when deinitting self

.. otherwise, when an AudioPWMOut object was deinitted without being
explicitly stop()ped, it would use up a slot in active_audio[]; the
5th iteration would create a non-working audio object which would just
buzz instead of playing the right thing.

Closes: #2203

ports/nrf/common-hal/audiopwmio/PWMAudioOut.c

@@ -194,6 +194,8 @@ void common_hal_audiopwmio_pwmaudioout_deinit(audiopwmio_pwmaudioout_obj_t* self
     if (common_hal_audiopwmio_pwmaudioout_deinited(self)) {
         return;
     }
+    deactivate_audiopwmout_obj(self);
+
     // TODO: ramp the pwm down from quiescent value to 0
     self->pwm->ENABLE = 0;