[media] videobuf2-core: call __setup_offsets only for mmap memory type

[media] videobuf2-core: call __setup_offsets only for mmap memory type

__setup_offsets fills the v4l2_planes' mem_offset fields, which is only valid
for V4L2_MEMORY_MMAP type buffers. For V4L2_MEMORY_DMABUF and _USERPTR buffers,
this incorrectly overwrites the fd and userptr fields.

Reported-by: Michael Olbrich <[email protected]>
Signed-off-by: Philipp Zabel <[email protected]>
Acked-by: Marek Szyprowski <[email protected]>
Acked-by: Pawel Osciak <[email protected]>
Acked-by: Hans Verkuil <[email protected]>
Signed-off-by: Mauro Carvalho Chehab <[email protected]>