[media] solo6x10: release vb2 buffers in solo_stop_streaming()

[media] solo6x10: release vb2 buffers in solo_stop_streaming()

Fixes warning that appears in dmesg after closing V4L2 userspace
application that plays video from the display device
(first device from V4L2 device nodes provided by solo, usually /dev/video0
when no other V4L2 devices are present). Encoder device nodes are not
affected. Can be reproduced by starting and closing

ffplay -f video4linux2  /dev/video0

[ 8130.281251] ------------[ cut here ]------------
[ 8130.281256] WARNING: CPU: 1 PID: 20414 at drivers/media/v4l2-core/videobuf2-core.c:1651 __vb2_queue_cancel+0x14b/0x230
[ 8130.281257] Modules linked in: ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat solo6x10 x86_pkg_temp_thermal vboxpci(O) vboxnetadp(O) vboxnetflt(O) vboxdrv(O)
[ 8130.281264] CPU: 1 PID: 20414 Comm: ffplay Tainted: G           O    4.10.0-gentoo #1
[ 8130.281264] Hardware name: ASUS All Series/B85M-E, BIOS 2301 03/30/2015
[ 8130.281265] Call Trace:
[ 8130.281267]  dump_stack+0x4f/0x72
[ 8130.281270]  __warn+0xc7/0xf0
[ 8130.281271]  warn_slowpath_null+0x18/0x20
[ 8130.281272]  __vb2_queue_cancel+0x14b/0x230
[ 8130.281273]  vb2_core_streamoff+0x23/0x90
[ 8130.281275]  vb2_streamoff+0x24/0x50
[ 8130.281276]  vb2_ioctl_streamoff+0x3d/0x50
[ 8130.281278]  v4l_streamoff+0x15/0x20
[ 8130.281279]  __video_do_ioctl+0x25e/0x2f0
[ 8130.281280]  video_usercopy+0x279/0x520
[ 8130.281282]  ? v4l_enum_fmt+0x1330/0x1330
[ 8130.281285]  ? unmap_region+0xdf/0x110
[ 8130.281285]  video_ioctl2+0x10/0x20
[ 8130.281286]  v4l2_ioctl+0xce/0xe0
[ 8130.281289]  do_vfs_ioctl+0x8b/0x5b0
[ 8130.281290]  ? __fget+0x72/0xa0
[ 8130.281291]  SyS_ioctl+0x74/0x80
[ 8130.281294]  entry_SYSCALL_64_fastpath+0x13/0x94
[ 8130.281295] RIP: 0033:0x7ff86fee6b27
[ 8130.281296] RSP: 002b:00007ffe467f6a08 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[ 8130.281297] RAX: ffffffffffffffda RBX: 00000000d1a4d788 RCX: 00007ff86fee6b27
[ 8130.281297] RDX: 00007ffe467f6a14 RSI: 0000000040045613 RDI: 0000000000000006
[ 8130.281298] RBP: 000000000373f8d0 R08: 00000000ffffffff R09: 00007ff860001140
[ 8130.281298] R10: 0000000000000243 R11: 0000000000000246 R12: 0000000000000000
[ 8130.281299] R13: 00000000000000a0 R14: 00007ffe467f6530 R15: 0000000001f32228
[ 8130.281300] ---[ end trace 00695dc96be646e7 ]---

Signed-off-by: Anton Sviridenko <anton@corp.bluecherry.net>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>