Consistently use spci_vm_id_t for VM ID.

Before we had a mix of spci_vm_id_t, uint32_t and uint64_t.

Change-Id: I7b51e48490f0f54064e1121242052873bddad2b5
diff --git a/inc/hf/vm.h b/inc/hf/vm.h
index 9548f2b..e35edc6 100644
--- a/inc/hf/vm.h
+++ b/inc/hf/vm.h
@@ -73,7 +73,7 @@
 };
 
 struct vm {
-	uint32_t id;
+	spci_vm_id_t id;
 	/** See api.c for the partial ordering on locks. */
 	struct spinlock lock;
 	uint32_t vcpu_count;