Add a workaround when scale for TENSOR_QUANT8_ASYMM is zero (#1605)

Add a workaround when scale for TENSOR_QUANT8_ASYMM is zero (#1605)

This patch adds a workaround, which changes `scale` to one when tensor's
scale is zero, because currently zero scale is passed down from TF Lite.
Note that the latest NeuralNetworks.h (see
https://android.googlesource.com/platform/frameworks/ml/+/master/nn/runtime/include/NeuralNetworks.h)
requires `scale` to be greater than zero.  Remove this workaround when
the scale value is correctly passed.

Signed-off-by: Sangmin Seo <sangmin7.seo@samsung.com>