[media] exynos4-is: Fix buffer release issue on fimc m2m video nodes

[media] exynos4-is: Fix buffer release issue on fimc m2m video nodes

This fixes dropping ownership of buffers in the driver's stop_streaming
callback, so buffers on the memory-to-memory video nodes are properly
released, also in case when the driver has a buffer only on one of the
queues (OUTPUT, CAPTURE) before the video node close.
The issue was being reported by videobuf2 with a following warning while
checking q->owned_by_drv_count:

[ 2498.310766] WARNING: CPU: 0 PID: 9358 at drivers/media/v4l2-core/videobuf2-core.c:1818 __vb2_queue_cancel+0xe8/0x14c
[ 2498.320258] Modules linked in:
[ 2498.323212] CPU: 0 PID: 9358 Comm: v4l2_decode Not tainted 4.7.0-rc4-next-20160627 #1210
[ 2498.331284] Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
[ 2498.331327] [<c010d738>] (unwind_backtrace) from [<c010a4b0>] (show_stack+0x10/0x14)
[ 2498.331344] [<c010a4b0>] (show_stack) from [<c031a4ac>] (dump_stack+0x74/0x94)
[ 2498.331358] [<c031a4ac>] (dump_stack) from [<c011a52c>] (__warn+0xd4/0x100)
[ 2498.331369] [<c011a52c>] (__warn) from [<c011a578>] (warn_slowpath_null+0x20/0x28)
[ 2498.331381] [<c011a578>] (warn_slowpath_null) from [<c04ed420>] (__vb2_queue_cancel+0xe8/0x14c)
[ 2498.331395] [<c04ed420>] (__vb2_queue_cancel) from [<c04ee10c>] (vb2_core_queue_release+0x18/0x38)
[ 2498.331406] [<c04ee10c>] (vb2_core_queue_release) from [<c04eab50>] (v4l2_m2m_ctx_release+0x1c/0x28)
[ 2498.331420] [<c04eab50>] (v4l2_m2m_ctx_release) from [<c04fe184>] (fimc_m2m_release+0x24/0x78)
[ 2498.331437] [<c04fe184>] (fimc_m2m_release) from [<c04d76c8>] (v4l2_release+0x34/0x74)
[ 2498.331455] [<c04d76c8>] (v4l2_release) from [<c01dc8d4>] (__fput+0x80/0x1bc)
[ 2498.331469] [<c01dc8d4>] (__fput) from [<c0132edc>] (task_work_run+0xc0/0xe4)
[ 2498.331482] [<c0132edc>] (task_work_run) from [<c011d460>] (do_exit+0x304/0xa24)
[ 2498.331493] [<c011d460>] (do_exit) from [<c011dccc>] (do_group_exit+0x3c/0xbc)
[ 2498.331505] [<c011dccc>] (do_group_exit) from [<c0126cac>] (get_signal+0x200/0x65c)
[ 2498.331517] [<c0126cac>] (get_signal) from [<c010e928>] (do_signal+0x84/0x3c4)
[ 2498.331532] [<c010e928>] (do_signal) from [<c010a0ec>] (do_work_pending+0xa4/0xb4)
[ 2498.331545] [<c010a0ec>] (do_work_pending) from [<c0107954>] (slow_work_pending+0xc/0x20)

Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>