Add , to clarify sentence.

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@15323 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

doc/swscale.txt

@@ -94,7 +94,7 @@ little headroom for convolutional filters like sharpening filters and
 minimizing SIMD instructions needed to apply them.
 It would be trivial to use a different 1.0 point if some specific scaler
 would benefit from it.
-Also as already hinted at initFilter() accepts an optional convolutional
+Also as already hinted at, initFilter() accepts an optional convolutional
 filter as input that can be used for contrast, saturation, blur, sharpening
 shift, chroma vs. luma shift, ...