media: cedrus: fix double free

If v4l2_ctrl_new_custom fails in cedrus_init_ctrls the error path will
free ctx->ctrls, which is also freed in cedrus release. Fix this by
setting ctx->ctrls to NULL instead of inadvertently removing kfree
calls.

Signed-off-by: Daniel Almeida <daniel.almeida@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>