caif_virtio: Remove redundant initialization of variable err

After commit a8c7687b ("caif_virtio: Check that vringh_config is not
null"), the variable err is being initialized with '-EINVAL' that is
meaningless. So remove it.

Signed-off-by: Jing Xiangfeng <jingxiangfeng@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>