slab: clean up the code comment in slab kmem_cache struct

In commit 3b0efdfa1e7 ("mm, sl[aou]b: Extract common fields from struct
kmem_cache") the variable 'obj_size' was moved above, however the
related code comment is not updated accordingly.  Do it here.

Link: http://lkml.kernel.org/r/20180603032402.27526-1-bhe@redhat.com
Signed-off-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/slab_def.h

@@ -67,9 +67,10 @@ struct kmem_cache {
 
 	/*
 	 * If debugging is enabled, then the allocator can add additional
-	 * fields and/or padding to every object. size contains the total
-	 * object size including these internal fields, the following two
-	 * variables contain the offset to the user object and its size.
+	 * fields and/or padding to every object. 'size' contains the total
+	 * object size including these internal fields, while 'obj_offset'
+	 * and 'object_size' contain the offset to the user object and its
+	 * size.
 	 */
 	int obj_offset;
 #endif /* CONFIG_DEBUG_SLAB */