Update SW scaler doc after libswscale commit 30841.

Patch by Janusz Krzysztofik jkrzyszt, tis icnet pl.

Originally committed as revision 22221 to svn://svn.ffmpeg.org/ffmpeg/trunk

doc/swscale.txt

@@ -30,7 +30,7 @@ slices, that is, consecutive non-overlapping rectangles of dimension
 
 special converter
     These generally are unscaled converters of common
-    formats, like YUV 4:2:0/4:2:2 -> RGB15/16/24/32. Though it could also
+    formats, like YUV 4:2:0/4:2:2 -> RGB12/15/16/24/32. Though it could also
     in principle contain scalers optimized for specific common cases.
 
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