[media] DocBook media: BT.2020 RGB uses limited quantization range

In contrast to all other colorspaces, the BT.2020 colorspace uses
limited range R'G'B' quantization as the default.

This was incorrected documented, so fix this.
Signed-off-by: NHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@osg.samsung.com>

Documentation/DocBook/media/v4l/pixfmt.xml

@@ -483,8 +483,8 @@ is the Y'CbCr encoding identifier (&v4l2-ycbcr-encoding;) to specify non-standar
 Y'CbCr encodings and the third is the quantization identifier (&v4l2-quantization;)
 to specify non-standard quantization methods. Most of the time only the colorspace
 field of &v4l2-pix-format; or &v4l2-pix-format-mplane; needs to be filled in. Note
-that the default R'G'B' quantization is always full range for all colorspaces,
-so this won't be mentioned explicitly for each colorspace description.</para>
+that the default R'G'B' quantization is full range for all colorspaces except for
+BT.2020 which uses limited range R'G'B' quantization.</para>
 
     <table pgwide="1" frame="none" id="v4l2-colorspace">
       <title>V4L2 Colorspaces</title>
@@ -598,7 +598,8 @@ so this won't be mentioned explicitly for each colorspace description.</para>
 	  <row>
 	    <entry><constant>V4L2_QUANTIZATION_DEFAULT</constant></entry>
 	    <entry>Use the default quantization encoding as defined by the colorspace.
-This is always full range for R'G'B' and usually limited range for Y'CbCr.</entry>
+This is always full range for R'G'B' (except for the BT.2020 colorspace) and usually
+limited range for Y'CbCr.</entry>
 	  </row>
 	  <row>
 	    <entry><constant>V4L2_QUANTIZATION_FULL_RANGE</constant></entry>
@@ -967,8 +968,8 @@ SMPTE 170M/BT.601. The Y'CbCr quantization is limited range.</para>
       <title id="col-bt2020">Colorspace BT.2020 (<constant>V4L2_COLORSPACE_BT2020</constant>)</title>
       <para>The <xref linkend="itu2020" /> standard defines the colorspace used by Ultra-high definition
 television (UHDTV). The default Y'CbCr encoding is <constant>V4L2_YCBCR_ENC_BT2020</constant>.
-The default Y'CbCr quantization is limited range. The chromaticities of the primary colors and
-the white reference are:</para>
+The default R'G'B' quantization is limited range (!), and so is the default Y'CbCr quantization.
+The chromaticities of the primary colors and the white reference are:</para>
       <table frame="none">
         <title>BT.2020 Chromaticities</title>
         <tgroup cols="3" align="left">