Kernel: Mark Lock getters as [[nodiscard]]

There is no reason to call a getter without observing the result, doing
so indicates an error in the code. Mark these methods as [[nodiscard]]
to find these cases.

Kernel/Lock.h

@@ -58,10 +58,10 @@ class Lock {
  void unlock();
  [[nodiscard]] Mode force_unlock_if_locked(u32&);
  void restore_lock(Mode, u32);
- bool is_locked() const { return m_mode != Mode::Unlocked; }
+ [[nodiscard]] bool is_locked() const { return m_mode != Mode::Unlocked; }
  void clear_waiters();
 
- const char* name() const { return m_name; }
+ [[nodiscard]] const char* name() const { return m_name; }
 
  static const char* mode_to_string(Mode mode)
  {
@@ -149,10 +149,10 @@ class Lockable {
  : m_resource(move(resource))
  {
  }
- Lock& lock() { return m_lock; }
- T& resource() { return m_resource; }
+ [[nodiscard]] Lock& lock() { return m_lock; }
+ [[nodiscard]] T& resource() { return m_resource; }
 
- T lock_and_copy()
+ [[nodiscard]] T lock_and_copy()
  {
  LOCKER(m_lock);
  return m_resource;