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>

drivers/video/omap2/omapfb/omapfb-main.c

diff --git a/drivers/video/omap2/omapfb/omapfb-main.c b/drivers/video/omap2/omapfb/omapfb-main.c
index a545e8d..db307e3 100644
--- a/drivers/video/omap2/omapfb/omapfb-main.c
+++ b/drivers/video/omap2/omapfb/omapfb-main.c
@@ -1271,6 +1271,9 @@
 	int do_update = 0;
 	int r = 0;
 
+	if (!display)
+		return -EINVAL;
+
 	omapfb_lock(fbdev);
 
 	switch (blank) {