video: fix doc warning

@mode has been renamed to
gst_video_decoder_set_interlaced_output_state() but not in the header
file, raising a doc warning.

Part-of: <gstreamer/gst-plugins-base!894>

gst-libs/gst/video/gstvideodecoder.h

@@ -459,7 +459,7 @@ GstVideoCodecState *gst_video_decoder_set_output_state (GstVideoDecoder *decoder
 
 GST_VIDEO_API
 GstVideoCodecState *gst_video_decoder_set_interlaced_output_state (GstVideoDecoder *decoder,
-                                                                   GstVideoFormat fmt, GstVideoInterlaceMode mode,
+                                                                   GstVideoFormat fmt, GstVideoInterlaceMode interlace_mode,
                                                                    guint width, guint height, GstVideoCodecState *reference);
 
 GST_VIDEO_API