doc: move sws_dither option description to scaler.texi

That's the more proper place where the scaler options should be
documented.

doc/filters.texi

@@ -6669,23 +6669,6 @@ Set full range (0-255 in case of 8-bit luma).
 Set "MPEG" range (16-235 in case of 8-bit luma).
 @end table
 
-@item sws_dither
-Set the dithering algorithm
-
-@table @samp
-@item auto
-Choose automatically.
-
-@item none
-No dithering
-
-@item bayer
-bayer dither
-
-@item ed
-error diffusion dither
-@end table
-
 @item force_original_aspect_ratio
 Enable decreasing or increasing output video width or height if necessary to
 keep the original aspect ratio. Possible values:

doc/scaler.texi

@@ -96,6 +96,24 @@ Set scaling algorithm parameters. The specified values are specific of
 some scaling algorithms and ignored by others. The specified values
 are floating point number values.
 
+@item sws_dither
+Set the dithering algorithm. Accepts one of the following
+values. Default value is @samp{auto}.
+
+@table @samp
+@item auto
+automatic choice
+
+@item none
+no dithering
+
+@item bayer
+bayer dither
+
+@item ed
+error diffusion dither
+@end table
+
 @end table
 
 @c man end SCALER OPTIONS