net/packet: remove dead code and unneeded variable from prb_setup_retire_blk_timer()

We test for 'tx_ring' being != zero and BUG() if that's the case. So after
that check there is no way that 'tx_ring' could be anything _but_ zero, so
testing it again is just dead code. Once that dead code is removed, the
'pkc' local variable becomes entirely redundant, so remove that as well.
Signed-off-by: NJesper Juhl <jj@chaosbits.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/packet/af_packet.c

@@ -516,13 +516,11 @@ static void prb_init_blk_timer(struct packet_sock *po,
 
 static void prb_setup_retire_blk_timer(struct packet_sock *po, int tx_ring)
 {
-	struct tpacket_kbdq_core *pkc;
-
 	if (tx_ring)
 		BUG();
 
-	pkc = tx_ring ? &po->tx_ring.prb_bdqc : &po->rx_ring.prb_bdqc;
-	prb_init_blk_timer(po, pkc, prb_retire_rx_blk_timer_expired);
+	prb_init_blk_timer(po, &po->rx_ring.prb_bdqc,
+			   prb_retire_rx_blk_timer_expired);
 }
 
 static int prb_calc_retire_blk_tmo(struct packet_sock *po,