tty: serial: move and cleanup vt8500_tx_empty()

Make vt8500_tx_empty() more readable by introducing a new local variable
and move the function before handle_tx(). That way we can reuse it in
there too.

Cc: <linux-arm-kernel@lists.infradead.org>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20220920052049.20507-2-jslaby@suse.czSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/vt8500_serial.c

@@ -187,6 +187,13 @@ static void handle_rx(struct uart_port *port)
 	tty_flip_buffer_push(tport);
 }
 
+static unsigned int vt8500_tx_empty(struct uart_port *port)
+{
+	unsigned int idx = vt8500_read(port, VT8500_URFIDX) & 0x1f;
+
+	return idx < 16 ? TIOCSER_TEMT : 0;
+}
+
 static void handle_tx(struct uart_port *port)
 {
 	struct circ_buf *xmit = &port->state->xmit;
@@ -201,7 +208,7 @@ static void handle_tx(struct uart_port *port)
 		return;
 	}
 
-	while ((vt8500_read(port, VT8500_URFIDX) & 0x1f) < 16) {
+	while (vt8500_tx_empty(port)) {
 		if (uart_circ_empty(xmit))
 			break;
 
@@ -260,12 +267,6 @@ static irqreturn_t vt8500_irq(int irq, void *dev_id)
 	return IRQ_HANDLED;
 }
 
-static unsigned int vt8500_tx_empty(struct uart_port *port)
-{
-	return (vt8500_read(port, VT8500_URFIDX) & 0x1f) < 16 ?
-						TIOCSER_TEMT : 0;
-}
-
 static unsigned int vt8500_get_mctrl(struct uart_port *port)
 {
 	unsigned int usr;