zmbv: remove memcpy() of decoded frame

Signed-off-by: Mans Rullgard <mans@mansr.com>

libavcodec/zmbv.c

@@ -574,7 +574,7 @@ static int decode_frame(AVCodecContext *avctx, void *data, int *data_size, AVPac
         default:
             av_log(avctx, AV_LOG_ERROR, "Cannot handle format %i\n", c->fmt);
         }
-        memcpy(c->prev, c->cur, c->width * c->height * (c->bpp / 8));
+        FFSWAP(uint8_t *, c->cur, c->prev);
     }
     *data_size = sizeof(AVFrame);
     *(AVFrame*)data = c->pic;