ffmpeg: replace log2 by av_log2

Slight change in output deemed irrelevant here.
Reviewed-by: Hendrik Leppkes <h.leppkes@gmail.com>
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>

ffmpeg.c

@@ -1560,7 +1560,7 @@ static void print_report(int is_last_report, int64_t timer_start, int64_t cur_ti
                 if (qp >= 0 && qp < FF_ARRAY_ELEMS(qp_histogram))
                     qp_histogram[qp]++;
                 for (j = 0; j < 32; j++)
-                    snprintf(buf + strlen(buf), sizeof(buf) - strlen(buf), "%X", (int)lrintf(log2(qp_histogram[j] + 1)));
+                    snprintf(buf + strlen(buf), sizeof(buf) - strlen(buf), "%X", av_log2(qp_histogram[j] + 1));
             }
 
             if ((enc->flags & AV_CODEC_FLAG_PSNR) && (ost->pict_type != AV_PICTURE_TYPE_NONE || is_last_report)) {