Revert "serial: mxc: have putc use the TXFIFO"

This reverts commit c7878a0483c59c48a730123bc0f4659fd40921bf.

Since commit c7878a0483c5 ("serial: mxc: have putc use the TXFIFO"),
serial console corruption can be seen when priting inside board_init().

Revert it to avoid the regression.

Reported-by: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Fabio Estevam <festevam@denx.de>
Acked-by: Tim Harvey <tharvey@gateworks.com>
diff --git a/drivers/serial/serial_mxc.c b/drivers/serial/serial_mxc.c
index 4cf79c1..82c0d84 100644
--- a/drivers/serial/serial_mxc.c
+++ b/drivers/serial/serial_mxc.c
@@ -311,7 +311,7 @@
 	struct mxc_serial_plat *plat = dev_get_plat(dev);
 	struct mxc_uart *const uart = plat->reg;
 
-	if (readl(&uart->ts) & UTS_TXFULL)
+	if (!(readl(&uart->ts) & UTS_TXEMPTY))
 		return -EAGAIN;
 
 	writel(ch, &uart->txd);