9p/trans_virtio: Remove sysfs file on probe failure

commit f997ea3b upstream.

This ensures we don't leak the sysfs file if we failed to
allocate chan->vc_wq during probe.

Link: http://lkml.kernel.org/r/20210517083557.172-1-xieyongji@bytedance.com
Fixes: 86c84373

 ("net/9p: Add sysfs mount_tag file for virtio 9P device")
Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>