libaml: resolve refs in ObjectType instruction

The standard states in section 19.5.93:

.... Notice that if this operation is performed
on an obeject reference such as one produced by
the Alias, Index, or RefOf statements, the obect
type of the base object is returned.

sys/src/libaml/aml.c

@@ -1800,7 +1800,7 @@ evalotype(void)
 	while(r != nil){
 		switch(TAG(r)){
 		case 'R': case 'A': case 'L':	/* Ref */
-			r = ((Ref*)r)->ref;
+			r = *((Ref*)r)->ptr;
 			continue;
 		case 'N':			/* Name */
 			r = ((Name*)r)->v;