Document return values of ABinderRpc_Accessor_delegateAccessor

Also changed the `OK` return value to `STATUS_OK` in the implementation.
The are both anonymous enums with the same value(0), but `STATUS_OK` is
intended to be used as a `binder_status_t`.

Test: na
Bug: 373660469
Change-Id: I66522047356e976bcaa08284b3c83bdb15374ff4
2 files changed