esp32_serial.c: Release the spinlock before calling uart_xmitchars, this

functions will call esp32_txint again which leads to deadlock since
esp32_txint has already locked the spinlock.

Signed-off-by: Abdelatif Guettouche <abdelatif.guettouche@espressif.com>

arch/xtensa/src/esp32/esp32_serial.c

@@ -1733,6 +1733,7 @@ static void esp32_txint(struct uart_dev_s *dev, bool enable)
            * interrupts disabled (note this may recurse).
            */
 
+          spin_unlock_irqrestore(&priv->lock, flags);
           uart_xmitchars(dev);
     #endif
         }