[media] doc-rst: Fix number of zeroed high order bits in 12-bit raw format defs

The number of high order bits in samples was documented to be 6 for 12-bit
data. This is clearly wrong, fix it.
Signed-off-by: NSakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: NHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/media/uapi/v4l/pixfmt-srggb12.rst

@@ -29,7 +29,7 @@ described as GRGR... BGBG..., RGRG... GBGB..., etc. Below is an example
 of one of these formats
 
 **Byte Order.**
-Each cell is one byte, high 6 bits in high bytes are 0.
+Each cell is one byte, high 4 bits in high bytes are 0.