aoe: Add forgotten NULL at end of attribute list in aoeblk.c

This caused the system to stall when the aoe module was loaded.  The
error was introduced in commit 4ca5224f3ea4779054d96e885ca9b3980801ce13

Signed-off-by: Dennis Stosberg <dennis@stosberg.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/block/aoe/aoeblk.c

@@ -68,6 +68,7 @@ static struct attribute *aoe_attrs[] = {
 	&disk_attr_mac.attr,
 	&disk_attr_netif.attr,
 	&disk_attr_fwver.attr,
+	NULL
 };
 
 static const struct attribute_group attr_group = {