mm/frontswap.c: fix the condition in BUG_ON

The largest index of swap device is MAX_SWAPFILES-1.  So the type should
be less than MAX_SWAPFILES.

Signed-off-by: Haifeng Li <omycle@gmail.com>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/frontswap.c

@@ -182,7 +182,7 @@ void __frontswap_init(unsigned type, unsigned long *map)
 	if (frontswap_ops)
 		frontswap_ops->init(type);
 	else {
-		BUG_ON(type > MAX_SWAPFILES);
+		BUG_ON(type >= MAX_SWAPFILES);
 		set_bit(type, need_init);
 	}
 }