Fix cloudbuilds of efr32. (#32818)

Change #32773 changed `openthread_mtd` to `openthread-mtd`.

Apply this change to cloudbuild yaml files as well.

Co-authored-by: Andrei Litvin <andreilitvin@google.com>

Author: andy31415

integrations/cloudbuild/smoke-test.yaml

@@ -75,8 +75,8 @@ steps:
               ./scripts/build/build_examples.py --enable-flashbundle
               --target efr32-brd4161a-light
               --target efr32-brd4161a-light-rpc
-              --target efr32-brd4161a-lock-openthread_mtd
-              --target efr32-brd4161a-lock-rpc-openthread_mtd
+              --target efr32-brd4161a-lock-openthread-mtd
+              --target efr32-brd4161a-lock-rpc-openthread-mtd
               --target efr32-brd4161a-unit-test
               build
               --create-archives /workspace/artifacts/