isdn: kcapi: avoid uninitialized data

gcc-7 points out that the AVMB1_ADDCARD ioctl results in an unintialized
value ending up in the cardnr parameter:

drivers/isdn/capi/kcapi.c: In function 'old_capi_manufacturer':
drivers/isdn/capi/kcapi.c:1042:24: error: 'cdef.cardnr' may be used uninitialized in this function [-Werror=maybe-uninitialized]
   cparams.cardnr = cdef.cardnr;

This has been broken since before the start of the git history, so
either the value is not used for anything important, or the ioctl
command doesn't get called in practice.

Setting the cardnr to zero avoids the warning and makes sure
we have consistent behavior.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/isdn/capi/kcapi.c

@@ -1032,6 +1032,7 @@ static int old_capi_manufacturer(unsigned int cmd, void __user *data)
 						     sizeof(avmb1_carddef))))
 				return -EFAULT;
 			cdef.cardtype = AVM_CARDTYPE_B1;
+			cdef.cardnr = 0;
 		} else {
 			if ((retval = copy_from_user(&cdef, data,
 						     sizeof(avmb1_extcarddef))))