[export] Use meta val from the old nodes in run_decompositions(). (#111225)
Summary: fall back to the old nodes when meta val is missing.
Test Plan: buck2 run //executorch/examples/portable/scripts:export -- --model_name=emformer_predict
Differential Revision: D50278439
Pull Request resolved: https://github.com/pytorch/pytorch/pull/111225
Approved by: https://github.com/larryliu0820
