serial: omap: fix DeviceTree boot

OMAP Architecture code, passes a few function
pointers for UART driver to use in order to
properly implement Power Management and Wakeup
capabilities.

The problem is that those function pointers,
which are passed (ab)using platform_data on
non-DT kernels, can't be passed down to drivers
through DT.

commit e5b57c03 (serial: omap: define helpers
for pdata function pointers) failed to take DT
kernels into consideration and caused a regression
to DT kernel boot.

Fix that by (re-)adding a check for valid pdata
pointer together with valid pdata->$FUNCTION
pointer.
Reported-by: NTony Lindgren <tony@atomide.com>
Signed-off-by: NFelipe Balbi <balbi@ti.com>
Tested-by: NTony Lindgren <tony@atomide.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/omap-serial.c

@@ -143,7 +143,7 @@ static int serial_omap_get_context_loss_count(struct uart_omap_port *up)
 {
 	struct omap_uart_port_info *pdata = up->dev->platform_data;
 
-	if (!pdata->get_context_loss_count)
+	if (!pdata || !pdata->get_context_loss_count)
 		return 0;
 
 	return pdata->get_context_loss_count(up->dev);
@@ -153,24 +153,30 @@ static void serial_omap_set_forceidle(struct uart_omap_port *up)
 {
 	struct omap_uart_port_info *pdata = up->dev->platform_data;
 
-	if (pdata->set_forceidle)
-		pdata->set_forceidle(up->dev);
+	if (!pdata || !pdata->set_forceidle)
+		return;
+
+	pdata->set_forceidle(up->dev);
 }
 
 static void serial_omap_set_noidle(struct uart_omap_port *up)
 {
 	struct omap_uart_port_info *pdata = up->dev->platform_data;
 
-	if (pdata->set_noidle)
-		pdata->set_noidle(up->dev);
+	if (!pdata || !pdata->set_noidle)
+		return;
+
+	pdata->set_noidle(up->dev);
 }
 
 static void serial_omap_enable_wakeup(struct uart_omap_port *up, bool enable)
 {
 	struct omap_uart_port_info *pdata = up->dev->platform_data;
 
-	if (pdata->enable_wakeup)
-		pdata->enable_wakeup(up->dev, enable);
+	if (!pdata || !pdata->enable_wakeup)
+		return;
+
+	pdata->enable_wakeup(up->dev, enable);
 }
 
 /*