esp32/machine_bitstream: Fix signal duplication on output pins.

After changing the bitstream implementation to use the RMT driver in
commit 72d86158121e32bbabaeade08f449d507bf40f9a
("esp32/machine_bitstream.c: Replace with RMT-based driver."), using
multiple `Neopixel` instances shows signal duplication between the
instances (i.e. a `write()` on one instance is written to all instances).

On invocation, the rmt driver configures the GPIO matrix to route the
output signal to the respective GPIO pin.  When called for a different
`NeoPixel` instance using a different pin, the new route is established,
but the old route still exists.  Now, the RMT output signal is sent to both
pins.

Fix this by setting the standard GPIO output function for the current pin
after uninstalling the RMT driver.

Signed-off-by: Simon Baatz <gmbnomis@gmail.com>

ports/esp32/machine_bitstream.c

@@ -133,6 +133,9 @@ void machine_bitstream_high_low(mp_hal_pin_obj_t pin, uint32_t *timing_ns, const
 
     // Uninstall the driver.
     check_esp_err(rmt_driver_uninstall(config.channel));
+
+    // Cancel RMT output to GPIO pin.
+    gpio_matrix_out(pin, SIG_GPIO_OUT_IDX, false, false);
 }
 
 #endif // MICROPY_PY_MACHINE_BITSTREAM