irda: small read past the end of array in debug code

The "reason" can come from skb->data[] and it hasn't been capped so it
can be from 0-255 instead of just 0-6.  For example in irlmp_state_dtr()
the code does:

	reason = skb->data[3];
	...
	irlmp_disconnect_indication(self, reason, skb);

Also LMREASON has a couple other values which don't have entries in the
irlmp_reasons[] array.  And 0xff is a valid reason as well which means
"unknown".

So far as I can see we don't actually care about "reason" except for in
the debug code.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>