[media] bdisp: fix debug info memory access

bdisp_dev->dbg.copy_node shall be a copy of (and not point to)
bdisp_ctx->node, since this resource is freed upon driver release.

Signed-off-by: Fabien Dessenne <fabien.dessenne@st.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>