Fix `RLimit` lock update

kernel/src/syscall/set_priority.rs

@@ -27,7 +27,7 @@ pub fn sys_set_priority(which: i32, who: u32, prio: i32, ctx: &Context) -> Resul
 
     let processes = get_processes(prio_target)?;
     for process in processes.iter() {
-        let rlimit = process.resource_limits().lock();
+        let rlimit = process.resource_limits();
         let limit = (rlimit.get_rlimit(RLIMIT_NICE).get_cur() as i8)
             .try_into()
             .map_err(|msg| Error::with_message(Errno::EINVAL, msg))?;