Fix pyre issue for diff train (#7336)

Summary:
Pull Request resolved: #7336

There's pyre issue introduced in D67262774. Fix it to unblock the diff train to land.

Reviewed By: JacobSzwejbka

Differential Revision: D67315650

Author: Martin Yuan

extension/llm/export/partitioner_lib.py

@@ -126,6 +126,7 @@ def _validate_ios_version() -> None:
         # On iPhone 15 Pro, CPU decode model is over 8x faster than GPU for stories110M,
         # so default to CPU_ONLY
         coreml_compute_units = "cpu_only"
+    # pyre-ignore
     coreml_compute_units = {
         "cpu_only": ct.ComputeUnit.CPU_ONLY,
         "cpu_and_ne": ct.ComputeUnit.CPU_AND_NE,