[media] DocBook media: fix number of bits filled with zeros for SRGBB12

The total number of bits is 16 (12+4). Fix it.
Signed-off-by: Andreas Weber <andy.weber.aw@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

Documentation/DocBook/media/v4l/pixfmt-srggb12.xml

@@ -18,7 +18,7 @@
 	<title>Description</title>
 
 	<para>The following four pixel formats are raw sRGB / Bayer formats with
-12 bits per colour. Each colour component is stored in a 16-bit word, with 6
+12 bits per colour. Each colour component is stored in a 16-bit word, with 4
 unused high bits filled with zeros. Each n-pixel row contains n/2 green samples
 and n/2 blue or red samples, with alternating red and blue rows. Bytes are
 stored in memory in little endian order. They are conventionally described