S5P: serial: Use the inline function instead of static value

Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>
diff --git a/drivers/serial/serial_s5p.c b/drivers/serial/serial_s5p.c
index 9c1cbf4..f1ffa29 100644
--- a/drivers/serial/serial_s5p.c
+++ b/drivers/serial/serial_s5p.c
@@ -72,7 +72,7 @@
 
 	writel(val / 16 - 1, &uart->ubrdiv);
 
-	if (use_divslot)
+	if (s5p_uart_divslot())
 		writew(udivslot[val % 16], &uart->rest.slot);
 	else
 		writeb(val % 16, &uart->rest.value);