Kernel: Rename Lock to Mutex

Let's be explicit about what kind of lock this is meant to be.

Kernel/Storage/StorageController.h

@@ -12,7 +12,7 @@
 #include <Kernel/Bus/PCI/DeviceController.h>
 #include <Kernel/Devices/Device.h>
 #include <Kernel/IO.h>
-#include <Kernel/Lock.h>
+#include <Kernel/Mutex.h>
 #include <Kernel/PhysicalAddress.h>
 #include <Kernel/Random.h>
 #include <Kernel/VM/PhysicalPage.h>