nfc/nci: fix race with opening and closing

Previously we leverage NCI_UNREG and the lock inside nci_close_device to
prevent the race condition between opening a device and closing a
device. However, it still has problem because a failed opening command
will erase the NCI_UNREG flag and allow another opening command to
bypass the status checking.

This fix corrects that by making sure the NCI_UNREG is held.

Reported-by:  <syzbot+43475bf3cfbd6e41f5b7@syzkaller.appspotmail.com>
Fixes: 48b71a9e ("NFC: add NCI_UNREG flag to eliminate the race")
Signed-off-by: Lin Ma <linma@zju.edu.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>