io_uring: documentation fixup

Fix incorrect name reference in comment. ki_filp does not exist in the
struct, but file does.

Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220224105157.1332353-1-dylany@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -830,7 +830,7 @@ enum {
  * NOTE! Each of the iocb union members has the file pointer
  * as the first entry in their struct definition. So you can
  * access the file pointer through any of the sub-structs,
- * or directly as just 'ki_filp' in this struct.
+ * or directly as just 'file' in this struct.
  */
 struct io_kiocb {
 	union {