Fix a bug in run.py related to model_analyzer
Summary: D41170045 (https://github.com/pytorch/benchmark/commit/022dfe3d89db9278119bf1cd179997076b5ec5b5) introduced a bug in run.py which references model_analyzer when it was not assigned if analyzer is not enabled.
Reviewed By: yuguo68
Differential Revision: D41202735
fbshipit-source-id: bb644ae8bff3cd7bca4517abc7c4b8c82c200db8
