[media] Fix small DocBook typo

Here is a small patch which fixes a DocBook mistake in the decoder_cmd
documentation.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/Documentation/DocBook/media/v4l/vidioc-decoder-cmd.xml b/Documentation/DocBook/media/v4l/vidioc-decoder-cmd.xml
index 466fe27..74b87f6 100644
--- a/Documentation/DocBook/media/v4l/vidioc-decoder-cmd.xml
+++ b/Documentation/DocBook/media/v4l/vidioc-decoder-cmd.xml
@@ -118,7 +118,7 @@
 	  <row>
             <entry></entry>
             <entry></entry>
-	    <entry>__u32</entry>
+	    <entry>__s32</entry>
 	    <entry><structfield>speed</structfield></entry>
             <entry>Playback speed and direction. The playback speed is defined as
 <structfield>speed</structfield>/1000 of the normal speed. So 1000 is normal playback.