Use enum PixelFormat to silence one icc warning:

warning #188: enumerated type mixed with another type
      enum PixelFormat pix_fmts[] = { c->pix_fmt, PIX_FMT_NONE };
                                      ^

Originally committed as revision 23640 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavfilter/vsrc_buffer.c

@@ -26,7 +26,8 @@ typedef struct {
     int64_t           pts;
     AVFrame           frame;
     int               has_frame;
-    int               h, w, pix_fmt;
+    int               h, w;
+    enum PixelFormat  pix_fmt;
     AVRational        pixel_aspect;
 } BufferSourceContext;