FB: sa1100: constify rgb structures

The rgb structures should only be read and never written.  Constify
them.

Acked-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/drivers/video/sa1100fb.h b/drivers/video/sa1100fb.h
index 1c3b459..7a3d66a 100644
--- a/drivers/video/sa1100fb.h
+++ b/drivers/video/sa1100fb.h
@@ -65,7 +65,7 @@
 struct sa1100fb_info {
 	struct fb_info		fb;
 	struct device		*dev;
-	struct sa1100fb_rgb	*rgb[NR_RGB];
+	const struct sa1100fb_rgb *rgb[NR_RGB];
 
 	u_int			max_bpp;
 	u_int			max_xres;