[qnnpack] Fix unused var warning when building for different archs. (#48730)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/48730
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Test Plan: CI
Reviewed By: kimishpatel
Differential Revision: D25273068
fbshipit-source-id: 3a0cea633bf1c02fa3176b3b3f43db46d2beb861
