media: tw686x: Fix oops on buffer alloc failure

[ Upstream commit 5a1a2f63d840dc2631505b607e11ff65ac1b7d3c ]

The error path currently calls tw686x_video_free() which requires
vc->dev to be initialized, causing a NULL dereference on uninitizalized
channels.

Fix this by setting the vc->dev fields for all the channels first.

Fixes: f8afaa8d ("[media] tw686x: Introduce an interface to support multiple DMA modes")

Signed-off-by: Krzysztof Ha?asa <khalasa@piap.pl>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>