OMAP: DSS2: OMAPFB: Remove redundant color register range check

Unsigned regno can never be less than zero. 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

@@ -1208,11 +1208,6 @@ static int _setcolreg(struct fb_info *fbi, u_int regno, u_int red, u_int green,
 		if (r != 0)
 			break;
 
-		if (regno < 0) {
-			r = -EINVAL;
-			break;
-		}
-
 		if (regno < 16) {
 			u16 pal;
 			pal = ((red >> (16 - var->red.length)) <<