ibmaem: prevent infinite probing loop on x3650 M2 systems

On older machines, probing for a nonexistent AEM interface returned an
IPMI error; when we saw this, we'd stop probing.  On the x3650 M2 and
(presumably) later, we are returned a value indicating success and a
buffer full of garbage or zeroes.  This causes the probe function to run
in an infinite loop.  To fix this, we add one last check--if the
interface number we're looking for is higher than the number of
interfaces that AEM claims to have, stop probing.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/hwmon/ibmaem.c

@@ -676,7 +676,8 @@ static int aem_find_aem2(struct aem_ipmi_data *data,
 		return -ETIMEDOUT;
 
 	if (data->rx_result || data->rx_msg_len != sizeof(*fi_resp) ||
-	    memcmp(&fi_resp->id, &system_x_id, sizeof(system_x_id)))
+	    memcmp(&fi_resp->id, &system_x_id, sizeof(system_x_id)) ||
+	    fi_resp->num_instances <= instance_num)
 		return -ENOENT;
 
 	return 0;