fbdev: propagate result of fb_videomode_from_videomode()

fb_videomode_from_videomode() may fail, but of_get_fb_videomode()
silently covers this fact. Instead, trow the error code to the
caller.
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/video/fbdev/core/fbmon.c

@@ -1475,7 +1475,9 @@ int of_get_fb_videomode(struct device_node *np, struct fb_videomode *fb,
 	if (ret)
 		return ret;
 
-	fb_videomode_from_videomode(&vm, fb);
+	ret = fb_videomode_from_videomode(&vm, fb);
+	if (ret)
+		return ret;
 
 	pr_debug("%s: got %dx%d display mode from %s\n",
 		of_node_full_name(np), vm.hactive, vm.vactive, np->name);