diracdec: fix full range videos

Full range video had been broken by the introduction of the < 2U check
at the following line. The bitstream format kind of implies that the full
and limited ranges use different pix_fmts but that's incorrect since we
have the avctx->color_range flag. So adjust the pixel range index to
be mapped to the same pix_fmts as limited range index.

Signed-off-by: Rostislav Pehlivanov <atomnuker@gmail.com>
