libutvideodec: Width and height don't need to be unsigned

Width and height, as used in utvideo_decode_frame, do not
need to be unsigned, and it could cause sign-compare
warnings later on.

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/libutvideo.cpp

@@ -130,7 +130,7 @@ static int utvideo_decode_frame(AVCodecContext *avctx, void *data,
 {
     UtVideoContext *utv = (UtVideoContext *)avctx->priv_data;
     AVFrame *pic = avctx->coded_frame;
-    unsigned int w = avctx->width, h = avctx->height;
+    int w = avctx->width, h = avctx->height;
 
     /* Set flags */
     pic->reference = 0;