NFC: Fix possible NULL ptr deref when getting the name of a socket

llcp_sock_getname() might get called before the LLCP socket was created.
This condition isn't checked, and llcp_sock_getname will simply deref a
NULL ptr in that case.

This exists starting with d646960f ("NFC: Initial LLCP support").
Signed-off-by: NSasha Levin <levinsasha928@gmail.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

net/nfc/llcp/sock.c

@@ -292,6 +292,9 @@ static int llcp_sock_getname(struct socket *sock, struct sockaddr *addr,
 
 	pr_debug("%p\n", sk);
 
+	if (llcp_sock == NULL)
+		return -EBADFD;
+
 	addr->sa_family = AF_NFC;
 	*len = sizeof(struct sockaddr_nfc_llcp);