Remove exit: return idiom from src/ble (#7518)

#### Problem

The `Exit` group of error-handling macros inhibit scoping, and
are unnecessary when there is no cleanup at the `exit:` label.

#### Change overview

- Remove `exit: return` idiom from `src/ble`, replacing `Exit` macros
  with corresponding `Return` macros.

#### Testing

No change to functionality; existing tests should catch regressions.