only enable query key scaling during fp16
jenkins jenkins jenkins jenkins jenkins jenkins
# What does this PR do ?

Add a one line overview of what this PR aims to accomplish.

Enable query key scaling only during fp16, since this is when TE enables query key scaling. https://github.com/NVIDIA/TransformerEngine/blob/666539f36275fa9c0fbc99f9ea50f2d6e29e336f/transformer_engine/pytorch/attention.py#L940 
