media: v4l2-mem2mem: Apply DST_QUEUE_OFF_BASE on MMAP buffers across ioctls

commit 8310ca94 upstream.

DST_QUEUE_OFF_BASE is applied to offset/mem_offset on MMAP capture buffers
only for the VIDIOC_QUERYBUF ioctl, while the userspace fields (including
offset/mem_offset) are filled in for VIDIOC_{QUERY,PREPARE,Q,DQ}BUF
ioctls. This leads to differences in the values presented to userspace.
If userspace attempts to mmap the capture buffer directly using values
from DQBUF, it will fail.

Move the code that applies the magic offset into a helper, and call
that helper from all four ioctl entry points.

[hverkuil: drop unnecessary '= 0' in v4l2_m2m_querybuf() for ret]

Fixes: 7f98639d ("V4L/DVB: add memory-to-memory device helper framework for videobuf")
Fixes: 908a0d7c ("[media] v4l: mem2mem: port to videobuf2")
Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
[OP: backport to 5.4: adjusted return logic in v4l2_m2m_qbuf() to match the
logic in the original commit: call v4l2_m2m_adjust_mem_offset() only if !ret
and before the v4l2_m2m_try_schedule() call]
Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>