h264: avoid calling get_format() multiple times

Some applications do not like that.
Fixes VDA
Reduces noise for VDPAU
Tested-by: Guillaume POIRIER <poirierg@gmail.com>
Tested-by: Carl Eugen Hoyos <cehoyos@ag.or.at>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/h264.c

@@ -2931,11 +2931,17 @@ static enum PixelFormat get_pixel_format(H264Context *h)
             return h->avctx->color_range == AVCOL_RANGE_JPEG ? AV_PIX_FMT_YUVJ422P
                                                              : AV_PIX_FMT_YUV422P;
         } else {
-            return h->avctx->get_format(h->avctx, h->avctx->codec->pix_fmts ?
+            int i;
+            const enum AVPixelFormat * fmt = h->avctx->codec->pix_fmts ?
                                         h->avctx->codec->pix_fmts :
                                         h->avctx->color_range == AVCOL_RANGE_JPEG ?
                                         hwaccel_pixfmt_list_h264_jpeg_420 :
-                                        ff_hwaccel_pixfmt_list_420);
+                                        ff_hwaccel_pixfmt_list_420;
+
+            for (i=0; fmt[i] != AV_PIX_FMT_NONE; i++)
+                if (fmt[i] == h->avctx->pix_fmt)
+                    return fmt[i];
+            return h->avctx->get_format(h->avctx, fmt);
         }
         break;
     default: