OMAP: DSS2: OMAPFB: Check fb2display() return value

Make sure NULL return value of fb2display() is not referenced. Found by
Coverity.

Signed-off-by: Jani Nikula <ext-jani.1.nikula@nokia.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@nokia.com>
diff --git a/drivers/video/omap2/omapfb/omapfb-ioctl.c b/drivers/video/omap2/omapfb/omapfb-ioctl.c
index d1f56d3..994f6a0 100644
--- a/drivers/video/omap2/omapfb/omapfb-ioctl.c
+++ b/drivers/video/omap2/omapfb/omapfb-ioctl.c
@@ -858,7 +858,7 @@
 			break;
 		}
 
-		if (!display->driver->enable_te) {
+		if (!display || !display->driver->enable_te) {
 			r = -ENODEV;
 			break;
 		}