Performance issue in the definition of build_search_images, nference/inference_wrapper.py(P1)

[DLPerf]

Hello, I found a performance issue in the definition of build_search_images, nference/inference_wrapper.py, tf.to_float(frame_sz[0:2] - 1) will be created repeatedly during program execution, resulting in reduced efficiency. I think it should be created before the loop.

Looking forward to your reply. Btw, I am very glad to create a PR to fix it if you are too busy.