[PyTorch] Fix typo in QNNPACK
Summary: Build failed when `PYTORCH_QNNPACK_RUNTIME_QUANTIZATION` is unset. According to D21339044 (https://github.com/pytorch/pytorch/commit/622f5b68f08eda6dd7eb6210494ea164d04ab399) it seems like a typo.
Test Plan: buck build //xplat/caffe2/aten/src/ATen/native/quantized/cpu/qnnpack:pytorch_qnnpackWindows xplat/mode/windows-msvc-15.9
Reviewed By: kimishpatel
Differential Revision: D26907439
fbshipit-source-id: ac52eeef4ee70726f2a97b22ae65921b39aa0c0b
