When a new video frame is started, the driver takes the next video buffer from
the list of active buffers and moves it to dev->usb_ctl.vid_buf / dev->usb_ctl.vbi_buf
for further processing.

On streaming stop we currently only give back the pending buffers from the list
but not the ones which are currently processed.

This causes the following warning from the vb2 core since kernel 3.15:

...
 ------------[ cut here ]------------
 WARNING: CPU: 1 PID: 2284 at drivers/media/v4l2-core/videobuf2-core.c:2115 __vb2_queue_cancel+0xed/0x150 [videobuf2_core]()
 [...]
 Call Trace:
  [<c0769c46>] dump_stack+0x48/0x69
  [<c0245b69>] warn_slowpath_common+0x79/0x90
  [<f925e4ad>] ? __vb2_queue_cancel+0xed/0x150 [videobuf2_core]
  [<f925e4ad>] ? __vb2_queue_cancel+0xed/0x150 [videobuf2_core]
  [<c0245bfd>] warn_slowpath_null+0x1d/0x20
  [<f925e4ad>] __vb2_queue_cancel+0xed/0x150 [videobuf2_core]
  [<f925fa35>] vb2_internal_streamoff+0x35/0x90 [videobuf2_core]
  [<f925fac5>] vb2_streamoff+0x35/0x60 [videobuf2_core]
  [<f925fb27>] vb2_ioctl_streamoff+0x37/0x40 [videobuf2_core]
  [<f8e45895>] v4l_streamoff+0x15/0x20 [videodev]
  [<f8e4925d>] __video_do_ioctl+0x23d/0x2d0 [videodev]
  [<f8e49020>] ? video_ioctl2+0x20/0x20 [videodev]
  [<f8e48c63>] video_usercopy+0x203/0x5a0 [videodev]
  [<f8e49020>] ? video_ioctl2+0x20/0x20 [videodev]
  [<c039d0e7>] ? fsnotify+0x1e7/0x2b0
  [<f8e49012>] video_ioctl2+0x12/0x20 [videodev]
  [<f8e49020>] ? video_ioctl2+0x20/0x20 [videodev]
  [<f8e4461e>] v4l2_ioctl+0xee/0x130 [videodev]
  [<f8e44530>] ? v4l2_open+0xf0/0xf0 [videodev]
  [<c0378de2>] do_vfs_ioctl+0x2e2/0x4d0
  [<c0368eec>] ? vfs_write+0x13c/0x1c0
  [<c0369a8f>] ? vfs_writev+0x2f/0x50
  [<c0379028>] SyS_ioctl+0x58/0x80
  [<c076fff3>] sysenter_do_call+0x12/0x12
 ---[ end trace 5545f934409f13f4 ]---
...

Many thanks to Hans Verkuil, whose recently added check in the vb2 core unveiled
this long standing issue and who has investigated it further.

Cc: <stable@vger.kernel.org>
Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>