assemble risc to it's position (not itself)

So in the next step the interpreter can use positions as program counter
and would be much more like the real thing

lib/risc/interpreter_platform.rb

@@ -19,10 +19,11 @@ module Risc
       4
     end
     def assemble(io)
-      io.write_unsigned_int_32(self)
+      pos = Position.get(self).at
+      io.write_unsigned_int_32(pos)
     end
     class Branch < Instruction
-      def first
+      def first #some logging assumes arm
         self
       end
     end

lib/risc/position.rb

@@ -62,7 +62,7 @@ module Risc
       case object
       when Parfait::BinaryCode
         CodePosition.new(object,at , extra)
-      when Arm::Instruction , Risc::Label
+      when Arm::Instruction , Risc::Instruction
         InstructionPosition.new(object,at , extra)
       else
         ObjectPosition.new(at,object)