helpers: prefix any helper with t_ instead of io_uring_

As brought up in an issue, this makes it confusing as to what could
potentially be liburing functions. Make it clear that these are test
helpers, hence use the t_ prefix for them.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/test/statx.c b/test/statx.c
index bd8b5a3..c0f9e9c 100644
--- a/test/statx.c
+++ b/test/statx.c
@@ -143,7 +143,7 @@
 		fname = argv[1];
 	} else {
 		fname = "/tmp/.statx";
-		io_uring_create_file(fname, 4096);
+		t_create_file(fname, 4096);
 	}
 
 	ret = test_statx(&ring, fname);