io_uring: fix warnings on shadow variables

There are a few of those:

io_uring/fdinfo.c:170:16: warning: declaration shadows a local variable [-Wshadow]
  170 |                 struct file *f = io_file_from_index(&ctx->file_table, i);
      |                              ^
io_uring/fdinfo.c:53:67: note: previous declaration is here
   53 | __cold void io_uring_show_fdinfo(struct seq_file *m, struct file *f)
      |                                                                   ^
io_uring/cancel.c:187:25: warning: declaration shadows a local variable [-Wshadow]
  187 |                 struct io_uring_task *tctx = node->task->io_uring;
      |                                       ^
io_uring/cancel.c:166:31: note: previous declaration is here
  166 |                              struct io_uring_task *tctx,
      |                                                    ^
io_uring/register.c:371:25: warning: declaration shadows a local variable [-Wshadow]
  371 |                 struct io_uring_task *tctx = node->task->io_uring;
      |                                       ^
io_uring/register.c:312:24: note: previous declaration is here
  312 |         struct io_uring_task *tctx = NULL;
      |                               ^

and a simple cleanup gets rid of them. For the fdinfo case, make a
distinction between the file being passed in (for the ring), and the
registered files we iterate. For the other two cases, just get rid of
shadowed variable, there's no reason to have a new one.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/cancel.c

@@ -184,9 +184,7 @@ static int __io_async_cancel(struct io_cancel_data *cd,
 	io_ring_submit_lock(ctx, issue_flags);
 	ret = -ENOENT;
 	list_for_each_entry(node, &ctx->tctx_list, ctx_node) {
-		struct io_uring_task *tctx = node->task->io_uring;
-
-		ret = io_async_cancel_one(tctx, cd);
+		ret = io_async_cancel_one(node->task->io_uring, cd);
 		if (ret != -ENOENT) {
 			if (!all)
 				break;

io_uring/fdinfo.c

@@ -50,9 +50,9 @@ static __cold int io_uring_show_cred(struct seq_file *m, unsigned int id,
  * Caller holds a reference to the file already, we don't need to do
  * anything else to get an extra reference.
  */
-__cold void io_uring_show_fdinfo(struct seq_file *m, struct file *f)
+__cold void io_uring_show_fdinfo(struct seq_file *m, struct file *file)
 {
-	struct io_ring_ctx *ctx = f->private_data;
+	struct io_ring_ctx *ctx = file->private_data;
 	struct io_overflow_cqe *ocqe;
 	struct io_rings *r = ctx->rings;
 	struct rusage sq_usage;

io_uring/register.c

@@ -368,8 +368,7 @@ static __cold int io_register_iowq_max_workers(struct io_ring_ctx *ctx,
 
 	/* now propagate the restriction to all registered users */
 	list_for_each_entry(node, &ctx->tctx_list, ctx_node) {
-		struct io_uring_task *tctx = node->task->io_uring;
-
+		tctx = node->task->io_uring;
 		if (WARN_ON_ONCE(!tctx->io_wq))
 			continue;