Add '-unstable' to solve ODR violation

The interface which is imported by an unstable interface is 'unstable'
as well. Until now, the ODR violation checker in aidl has omitted an
interface imported, but it will be checked, accordingly, fix the current
problem

Bug: 146436251
Test: m nothing
Change-Id: I3a9ae6e17e49c731e825ef00b9b9574c3f2e2719
Merged-In: I3a9ae6e17e49c731e825ef00b9b9574c3f2e2719
Exempt-From-Owner-Approval: cp from internal