io_uring: Fix use of uninitialized ret in io_eventfd_register()

Clang warns:

  fs/io_uring.c:9396:9: warning: variable 'ret' is uninitialized when used here [-Wuninitialized]
          return ret;
                 ^~~
  fs/io_uring.c:9373:13: note: initialize the variable 'ret' to silence this warning
          int fd, ret;
                     ^
                      = 0
  1 warning generated.

Just return 0 directly and reduce the scope of ret to the if statement,
as that is the only place that it is used, which is how the function was
before the fixes commit.

Fixes: 1a75fac9a0f9 ("io_uring: avoid ring quiesce while registering/unregistering eventfd")
Link: https://github.com/ClangBuiltLinux/linux/issues/1579Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/r/20220207162410.1013466-1-nathan@kernel.orgSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -9378,7 +9378,7 @@ static int io_eventfd_register(struct io_ring_ctx *ctx, void __user *arg,
 {
 	struct io_ev_fd *ev_fd;
 	__s32 __user *fds = arg;
-	int fd, ret;
+	int fd;
 
 	ev_fd = rcu_dereference_protected(ctx->io_ev_fd,
 					lockdep_is_held(&ctx->uring_lock));
@@ -9394,14 +9394,14 @@ static int io_eventfd_register(struct io_ring_ctx *ctx, void __user *arg,
 
 	ev_fd->cq_ev_fd = eventfd_ctx_fdget(fd);
 	if (IS_ERR(ev_fd->cq_ev_fd)) {
-		ret = PTR_ERR(ev_fd->cq_ev_fd);
+		int ret = PTR_ERR(ev_fd->cq_ev_fd);
 		kfree(ev_fd);
 		return ret;
 	}
 	ev_fd->eventfd_async = eventfd_async;
 
 	rcu_assign_pointer(ctx->io_ev_fd, ev_fd);
-	return ret;
+	return 0;
 }
 
 static void io_eventfd_put(struct rcu_head *rcu)