Fixed n3ds build

(cherry picked from commit d95dbe78bb)

src/joystick/SDL_joystick.c

@@ -144,9 +144,9 @@ SDL_bool SDL_JoysticksQuitting(void)
 
 void SDL_LockJoysticks(void)
 {
-    SDL_AtomicIncRef(&SDL_joystick_lock_pending);
+    (void)SDL_AtomicIncRef(&SDL_joystick_lock_pending);
     SDL_LockMutex(SDL_joystick_lock);
-    SDL_AtomicDecRef(&SDL_joystick_lock_pending);
+    (void)SDL_AtomicDecRef(&SDL_joystick_lock_pending);
 
     ++SDL_joysticks_locked;
 }