media: videobuf2-dma-sg: Fix buf->vb NULL pointer dereference

media: videobuf2-dma-sg: Fix buf->vb NULL pointer dereference

Commit a4b83deb3e76 ("media: videobuf2: rework vb2_mem_ops API")
added a new vb member to struct vb2_dma_sg_buf, but it only added
code setting this to the vb2_dma_sg_alloc() function and not to the
vb2_dma_sg_get_userptr() and vb2_dma_sg_attach_dmabuf() which also
create vb2_dma_sg_buf objects.

This is causing a crash due to a NULL pointer deref when using
libcamera on devices with an Intel IPU3 (qcam app).

Fix these crashes by assigning buf->vb in the other 2 functions too,
note libcamera tests the vb2_dma_sg_get_userptr() path, the change
to the vb2_dma_sg_attach_dmabuf() path is untested.

Fixes: a4b83deb3e76 ("media: videobuf2: rework vb2_mem_ops API")
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>