MPS: mobilebert inference error

[guangy10]

🐛 Describe the bug

mobilebert+mps has been failing consistently: https://github.com/pytorch/executorch/actions/workflows/apple-perf.yml?query=event%3Aschedule

We will disable this model from continuous benchmarking and track the bug/fix here.

The stacktrace:

  Test Case '-[GenericTests test_load_mobilebert_mps_float16_pte_iOS_17_2_1_iPhone15_4]' started.
  loc("addmm/beta*bias*alpha*matmul_6"("(mpsFileLoc): /Library/Caches/com.apple.xbs/Sources/MetalPerformanceShadersGraph/mpsgraph/MetalPerformanceShadersGraph/Core/Files/MPSGraphUtilities.mm":233:0)): error: input types 'tensor<8x128xf32>' and 'tensor<128xf16>' are not broadcast compatible
  LLVM ERROR: Failed to infer result type(s).

Job link: https://github.com/pytorch/executorch/actions/runs/12920386457/job/36038669108#step:14:2107

Versions

trunk

[guangy10]

cc: @kimishpatel @cbilgin @cccclai Can you tag the right PoC from MPS team to take a look?

[kimishpatel]

@kulinseth @DenisVieriu97