stm32_serial.c: Don't fake a TX interrupt when interrupts are not

suppressed.

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

arch/arm/src/stm32/stm32_serial.c

@@ -2964,6 +2964,7 @@ static void up_txint(struct uart_dev_s *dev, bool enable)
 
       up_restoreusartint(priv, ie);
 
+#else
       /* Fake a TX interrupt here by just calling uart_xmitchars() with
        * interrupts disabled (note this may recurse).
        */