Kernel: Fix PriorityMutex::try_lock()

Forgot to check this when I updated Mutex::try_lock()

kernel/include/kernel/Lock/Mutex.h

@@ -103,6 +103,7 @@ namespace Kernel
 				ASSERT(m_lock_depth == 0);
 			}
 			m_lock_depth++;
+			return true;
 		}
 
 		void unlock()