MLBEDSW-10199: Normalize quantization before checking OFM Rescale fusing

On Ethos-U55 and Ethos-U65, only Rescales with unit scale can be fused
to Minimum operators. However, the output quantization shift was not
normalized to zero before checking if the scale was unit or not.

Change-Id: If8e04034045853e0c7b715547b2a68609c11cbe1
Signed-off-by: Rickard Bolin <rickard.bolin@arm.com>