Don't write LFN entries for "." and ".."

When checking a filesystem with fsck.fat it repport errors and removes the
LFN entries for "." and "..".
Also, the linux vfat fs is not creating LFN entries for "." and "..".

fix MabezDev#12

embedded-fatfs/src/dir.rs

@@ -693,8 +693,15 @@ impl<'a, IO: ReadWriteSeek, TP: TimeProvider, OCC: OemCpConverter> Dir<'a, IO, T
         validate_long_name(name)?;
         // convert long name to UTF-16
         let lfn_utf16 = Self::encode_lfn_utf16(name);
-        // write LFN entries
-        let (mut stream, start_pos) = self.alloc_and_write_lfn_entries(&lfn_utf16, raw_entry.name()).await?;
+        let (mut stream, start_pos) = if name == "." || name == ".." {
+            // skip LFN entries for "." and ".." and only find space 1 SFN entry
+            let mut stream = self.find_free_entries(1).await?;
+            let start_pos = stream.seek(io::SeekFrom::Current(0)).await?;
+            (stream, start_pos)
+        } else {
+            // write LFN entries
+            self.alloc_and_write_lfn_entries(&lfn_utf16, raw_entry.name()).await?
+        };
         // write short name entry
         raw_entry.serialize(&mut stream).await?;
         // Get position directory stream after entries were written