Reinterpret results as unsigned if the tf is unsigned

If tf/tfl results are unsigned, then recast ref model
results to the same data type as tf/tfl results before
comparison

This change allows tosa to use signless integers when
stripping out quantized data types

Signed-off-by: Tai Ly <tai.ly@arm.com>
Change-Id: I328af946140e1a9f45ce5d3b93145d64a8e0780f