hdl/modules/position_calc/virtex6/*: fix sum output

The sum position data was wrongly truncated and its
value was wrong. A reiterpret block was added before
the cast block to correct this.
hdl/modules/position_calc/artix7/*: fix sum output

The sum position data was wrongly truncated and its
value was wrong. A reiterpret block was added before
the cast block to correct this.
models/*: fix model to fix sum output at various rates