linux/slab.h: fix three off-by-one typos in comment

The first is a keyboard-off-by-one, the other two the ordinary mathy kind.
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/slab.h

@@ -262,8 +262,8 @@ extern struct kmem_cache *kmalloc_dma_caches[KMALLOC_SHIFT_HIGH + 1];
  * belongs to.
  * 0 = zero alloc
  * 1 =  65 .. 96 bytes
- * 2 = 120 .. 192 bytes
- * n = 2^(n-1) .. 2^n -1
+ * 2 = 129 .. 192 bytes
+ * n = 2^(n-1)+1 .. 2^n
  */
 static __always_inline int kmalloc_index(size_t size)
 {