radix-tree: fix the comment of radix_tree_next_slot()

fix the comment of radix_tree_next_slot():
interator --> iterator.
Signed-off-by: Hui Su <sh_def@163.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

include/linux/radix-tree.h

@@ -377,7 +377,7 @@ radix_tree_chunk_size(struct radix_tree_iter *iter)
  * radix_tree_next_slot - find next slot in chunk
  *
  * @slot:	pointer to current slot
- * @iter:	pointer to interator state
+ * @iter:	pointer to iterator state
  * @flags:	RADIX_TREE_ITER_*, should be constant
  * Returns:	pointer to next slot, or NULL if there no more left
  *