caif_virtio: fix wrong pointer check in cfv_probe()

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().

Fixes: 0d2e1a2926b1 ("caif_virtio: Introduce caif over virtio")
Signed-off-by: Vitaliy Shevtsov <v.shevtsov@mt-integration.ru>
Reviewed-by: Gerhard Engleder <gerhard@engleder-embedded.com>
Link: https://patch.msgid.link/20250227184716.4715-1-v.shevtsov@mt-integration.ru
Signed-off-by: Jakub Kicinski <kuba@kernel.org>