bluetooth: fix warning in net/bluetooth/rfcomm/sock.c

fix this warning:

  net/bluetooth/rfcomm/sock.c: In function ‘rfcomm_sock_ioctl’:
  net/bluetooth/rfcomm/sock.c:795: warning: unused variable ‘sk’

perhaps BT_DEBUG() should be improved to do printf format checking
instead of the #ifdef, but that looks quite intrusive: each bluetooth
.c file undefines the macro.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/bluetooth/rfcomm/sock.c

@@ -792,7 +792,9 @@ static int rfcomm_sock_getsockopt(struct socket *sock, int level, int optname, c
 
 static int rfcomm_sock_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
 {
+#if defined(CONFIG_BT_RFCOMM_TTY) || defined(CONFIG_BT_RFCOMM_DEBUG)
 	struct sock *sk = sock->sk;
+#endif
 	int err;
 
 	BT_DBG("sk %p cmd %x arg %lx", sk, cmd, arg);