[media] v4l: Fix colorspace conversion error in sample code

The sample code erroneously scales the y1, pb and pr variables from the
[0.0 .. 1.0] and [-0.5 .. 0.5] ranges to [0 .. 255] and [-128 .. 127].
Fix it.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: NHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: NMauro Carvalho Chehab <m.chehab@samsung.com>

Documentation/DocBook/media/v4l/pixfmt.xml

@@ -391,9 +391,9 @@ clamp (double x)
 	else               return r;
 }
 
-y1 = (255 / 219.0) * (Y1 - 16);
-pb = (255 / 224.0) * (Cb - 128);
-pr = (255 / 224.0) * (Cr - 128);
+y1 = (Y1 - 16) / 219.0;
+pb = (Cb - 128) / 224.0;
+pr = (Cr - 128) / 224.0;
 
 r = 1.0 * y1 + 0     * pb + 1.402 * pr;
 g = 1.0 * y1 - 0.344 * pb - 0.714 * pr;