mISDN: positive error return should be negative in mode_hfcmulti()

The error return should be negative.  Its only caller that acts upon its
return, handle_bmsg(), transmits the positive error but can also return
negative errors.
Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
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

@@ -2846,7 +2846,7 @@ mode_hfcmulti(struct hfc_multi *hc, int ch, int protocol, int slot_tx,
 	int conf;
 
 	if (ch < 0 || ch > 31)
-		return EINVAL;
+		return -EINVAL;
 	oslot_tx = hc->chan[ch].slot_tx;
 	oslot_rx = hc->chan[ch].slot_rx;
 	conf = hc->chan[ch].conf;