Kernel/PCI: Verify Access is not initialized before initializing it

There's no valid case where we should try to initialize the Access
singleton multiple times, therefore just assert if it ever happens.

Kernel/Bus/PCI/Access.cpp

@@ -88,9 +88,7 @@ UNMAP_AFTER_INIT bool Access::find_and_register_pci_host_bridges_from_acpi_mcfg_
 
 UNMAP_AFTER_INIT bool Access::initialize_for_multiple_pci_domains(PhysicalAddress mcfg_table)
 {
-    if (Access::is_initialized())
-        return false;
-
+    VERIFY(!Access::is_initialized());
     auto* access = new Access();
     if (!access->find_and_register_pci_host_bridges_from_acpi_mcfg_table(mcfg_table))
         return false;
@@ -101,9 +99,7 @@ UNMAP_AFTER_INIT bool Access::initialize_for_multiple_pci_domains(PhysicalAddres
 
 UNMAP_AFTER_INIT bool Access::initialize_for_one_pci_domain()
 {
-    if (Access::is_initialized()) {
-        return false;
-    }
+    VERIFY(!Access::is_initialized());
     auto* access = new Access();
     auto host_bridge = HostBridge::must_create_with_io_access();
     access->add_host_controller(move(host_bridge));