avformat/matroska: fix MatroskaVideoFieldOrder enum values

The spec says

9: Interlaced with bottom field displayed first and top field stored first
14: Interlaced with top field displayed first and bottom field stored first

And avcodec.h states

AV_FIELD_TB,          //< Top coded first, bottom displayed first
AV_FIELD_BT,          //< Bottom coded first, top displayed first

Reviewed-by: Dave Rice <dave@dericed.com>
Signed-off-by: James Almer <jamrial@gmail.com>

libavformat/matroska.h

@@ -286,8 +286,8 @@ typedef enum {
     MATROSKA_VIDEO_FIELDORDER_UNDETERMINED = 2,
     MATROSKA_VIDEO_FIELDORDER_TT           = 1,
     MATROSKA_VIDEO_FIELDORDER_BB           = 6,
-    MATROSKA_VIDEO_FIELDORDER_BT           = 9,
+    MATROSKA_VIDEO_FIELDORDER_TB           = 9,
-    MATROSKA_VIDEO_FIELDORDER_TB           = 14,
+    MATROSKA_VIDEO_FIELDORDER_BT           = 14,
 } MatroskaVideoFieldOrder;
 
 typedef enum {