x86, highmem_32.c: Clean up comment

Signed-off-by: NFigo.zhang <figo1802@gmail.com>
Cc: Andrew Morton <akpm@osdl.org>
LKML-Reference: <1246248175.5759.12.camel@myhost>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/mm/highmem_32.c

@@ -24,7 +24,7 @@ void kunmap(struct page *page)
  * no global lock is needed and because the kmap code must perform a global TLB
  * invalidation when the kmap pool wraps.
  *
- * However when holding an atomic kmap is is not legal to sleep, so atomic
+ * However when holding an atomic kmap it is not legal to sleep, so atomic
  * kmaps are appropriate for short, tight code paths only.
  */
 void *kmap_atomic_prot(struct page *page, enum km_type type, pgprot_t prot)