media: videobuf2: forbid remove_bufs when legacy fileio is active

media: videobuf2: forbid remove_bufs when legacy fileio is active

vb2_ioctl_remove_bufs() call manipulates queue internal buffer list,
potentially overwriting some pointers used by the legacy fileio access
mode. Forbid that ioctl when fileio is active to protect internal queue
state between subsequent read/write calls.

CC: stable@vger.kernel.org
Fixes: a3293a85381e ("media: v4l2: Add REMOVE_BUFS ioctl")
Reported-by: Shuangpeng Bai <SJB7183@psu.edu>
Closes: https://lore.kernel.org/linux-media/5317B590-AAB4-4F17-8EA1-621965886D49@psu.edu/
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>