io_uring: fix user_data field name in comment

io_uring_cqe's user_data field refers to `sqe->data`, but io_uring_sqe
does not have a data field. Fix the comment to say `sqe->user_data`.
Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Link: https://github.com/axboe/liburing/pull/1206
Link: https://lore.kernel.org/r/20240816181526.3642732-1-csander@purestorage.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

include/uapi/linux/io_uring.h

@@ -421,7 +421,7 @@ enum io_uring_msg_ring_flags {
  * IO completion data structure (Completion Queue Entry)
  */
 struct io_uring_cqe {
-	__u64	user_data;	/* sqe->data submission passed back */
+	__u64	user_data;	/* sqe->user_data value passed back */
 	__s32	res;		/* result code for this event */
 	__u32	flags;