quant primitives: always set min val for scale

[jerryzh168]

Summary:
This is to avoid div by 0 in quantize

Test Plan:
python test/quantization/test_quant_primitives.py -k test_choose_qparams_tensor_asym_eps

Reviewers:

Subscribers:

Tasks:

Tags:

[cpuhrsch]

Just see what happens if eps is less than machine epsilon and if clamp throws a warning etc.

Otherwise we might want to add a warning/exception if user passes an eps below scalar machine epsilon (else we divide by zero later).