media: pci: cx23885: check cx23885_vdev_init() return

cx23885_vdev_init() can return a NULL pointer, but that pointer
is used in the next line without a check.

Add a NULL pointer check and go to the error unwind if it is NULL.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reported-by: Sicong Huang <huangsicong@iie.ac.cn>