build: Allow unread fields in structs

Signed-off-by: Akira Moroo <retrage01@gmail.com>

Author: retrage

src/efi/file.rs

@@ -136,6 +136,7 @@ pub extern "win64" fn set_position(_: *mut FileProtocol, _: u64) -> Status {
     Status::UNSUPPORTED
 }
 
+#[allow(unused)]
 struct FileInfo {
     size: u64,
     file_size: u64,

src/fat.rs

@@ -104,6 +104,7 @@ pub struct Filesystem<'a> {
     first_fat_sector: u32,
     first_data_sector: u32,
     data_sector_count: u32,
+    #[allow(unused)]
     data_cluster_count: u32,
     root_cluster: u32, // FAT32 only
 }