config: remove unnecessary mut

src/runtime/src/config.rs

@@ -77,7 +77,7 @@ impl Config {
         Ok(Config { fs })
     }
 
-    fn read<'b>(&mut self, key: &'b str) -> Result<'b, Vec<u8>> {
+    fn read<'b>(&self, key: &'b str) -> Result<'b, Vec<u8>> {
         let root_dir = self.fs.root_dir();
         let mut buffer: Vec<u8> = Vec::new();
         match root_dir.open_file(&["/CONFIG/", key, ".BIN"].concat()) {
@@ -90,7 +90,7 @@ impl Config {
         Ok(buffer)
     }
 
-    pub fn read_str<'b>(&mut self, key: &'b str) -> Result<'b, String> {
+    pub fn read_str<'b>(&self, key: &'b str) -> Result<'b, String> {
         Ok(String::from_utf8(self.read(key)?)?)
     }
 }