[hvdcp_opti] Fix ReadWriteBytesFile so it actually stores data

Bug: 465183573

Test: tested on Sorrel that qbg_context is not empty

Change-Id: I4d00c3188bedf8cc5cf1ad9d1cc006dfb2c0188c
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1442488
Commit-Queue: Ruby Zhuang <rdzhuang@google.com>
Reviewed-by: Benjamin Lerman <qsr@google.com>

Author: Ruby Zhuang

src/starnix/modules/hvdcp_opti/utils.rs

@@ -40,7 +40,7 @@ pub struct ReadWriteBytesFile {
 
 impl ReadWriteBytesFile {
     pub fn new_node() -> impl FsNodeOps {
-        SimpleFileNode::new(move || Ok(BytesFile::new(Self::default())))
+        BytesFile::new_node(Self::default())
     }
 }