sc->data_size may contain the size of a single fragment after probing, and
using it alongside the duration of the entire stream to calculate bitrate
will result in a bogus small value.

Before:
  Duration: 00:00:05.00, start: 0.000000, bitrate: 586 kb/s
  Stream #0:0[0x1](und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(progressive), 640x360 [SAR 1:1 DAR 16:9], 112 kb/s, 60 fps, 60 tbr, 15360 tbn (default)

After:
  Duration: 00:00:05.00, start: 0.000000, bitrate: 586 kb/s
  Stream #0:0[0x1](und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(progressive), 640x360 [SAR 1:1 DAR 16:9], 561 kb/s, 60 fps, 60 tbr, 15360 tbn (default)
Signed-off-by: James Almer <jamrial@gmail.com>