Convert enum fields to upper snakecase.

Change-Id: I0fb65ecf523b3e5303344737c54bbe82c5e93ee0
diff --git a/src/vm.c b/src/vm.c
index d1fb5bb..532d5a2 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -44,7 +44,7 @@
 
 	vm->id = vm_count;
 	vm->vcpu_count = vcpu_count;
-	vm->mailbox.state = mailbox_state_empty;
+	vm->mailbox.state = MAILBOX_STATE_EMPTY;
 	atomic_init(&vm->aborting, false);
 
 	if (!mm_vm_init(&vm->ptable, ppool)) {