caif_virtio: fix wrong pointer check in cfv_probe()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: caif_virtio: fix wrong pointer check in cfv_probe() del_vqs() frees virtqueues, therefore cfv->vq_tx pointer should be checked for NULL before calling it, not cfv->vdev. Also the current implementation is redundant because the pointer cfv->vdev is dereferenced before it is checked for NULL. Fix this by checking cfv->vq_tx for NULL instead of cfv->vdev before calling del_vqs().

References

• https://git.kernel.org/stable/c/990fff6980d0c1693d60a812f58dbf93eab0473f
• https://git.kernel.org/stable/c/7b5fe58959822e6cfa884327cabba6be3b01883d
• https://git.kernel.org/stable/c/8e4e08ca4cc634b337bb74bc9a70758fdeda0bcb
• https://git.kernel.org/stable/c/29e0cd296c87240278e2f7ea4cf3f496b60c03af
• https://git.kernel.org/stable/c/90d302619ee7ce5ed0c69c29c290bdccfde66418
• https://git.kernel.org/stable/c/56cddf71cce3b15b078e937fadab29962b6f6643
• https://git.kernel.org/stable/c/597c27e5f04cb50e56cc9aeda75d3e42b6b89c3e
• https://git.kernel.org/stable/c/a466fd7e9fafd975949e5945e2f70c33a94b1a70