doc/filters/scale: fix MAN rendering of @ref arguments

doc/filters.texi

@@ -6597,7 +6597,8 @@ Default value is @samp{0}.
 @item flags
 Set libswscale scaling flags. If not explictly specified the filter
 applies a bilinear scaling algorithm.
-See the @ref{sws_flags,,,ffmpeg-scaler.texi} for the values.
+See @ref{sws_flags,,the ffmpeg-scaler manual,ffmpeg-scaler} for
+the complete list of values.
 
 @item size, s
 Set the video size, the value must be a valid abbreviation or in the