drivers/isdn: eliminate duplicated test

The code checked slot_rx twice.  Check slot_tx by analogy with the bank
case.

The semantic match that finds this problem is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@
expression E;
@@

(
*E && E
|
*E || E
)
// </smpl>
Signed-off-by: Julia Lawall <julia@diku.dk>
Cc: Karsten Keil <isdn@linux-pingi.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/isdn/hardware/mISDN/hfcmulti.c

@@ -3152,7 +3152,7 @@ static void
 hfcmulti_pcm(struct hfc_multi *hc, int ch, int slot_tx, int bank_tx,
     int slot_rx, int bank_rx)
 {
-	if (slot_rx < 0 || slot_rx < 0 || bank_tx < 0 || bank_rx < 0) {
+	if (slot_tx < 0 || slot_rx < 0 || bank_tx < 0 || bank_rx < 0) {
 		/* disable PCM */
 		mode_hfcmulti(hc, ch, hc->chan[ch].protocol, -1, 0, -1, 0);
 		return;