[media] v4l2-ctrls.c: fix RGB quantization range control menu

All control menus use the english capitalization rules of titles.

The only menu not following these rules is the RGB Quantization Range control
menu. Fix this.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>