video: of_display_timing.h: include errno.h

If CONFIG_OF is not enabled, default of_get_display_timing() returns an
errno, so include the header.

Fixes: 422b67e0b3 ("videomode: provide dummy inline functions for !CONFIG_OF")
Suggested-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Helge Deller <deller@gmx.de>

include/video/of_display_timing.h

@@ -8,6 +8,8 @@
 #ifndef __LINUX_OF_DISPLAY_TIMING_H
 #define __LINUX_OF_DISPLAY_TIMING_H
 
+#include <linux/errno.h>
+
 struct device_node;
 struct display_timing;
 struct display_timings;