hal: update active_input after usecase is removed from list

update active_input only after the usecase that is being
stopped is removed from the usecase list. Otherwise,
active_input can be set to the same usecase that is being
terminated and input stream deallocated. At that point
members of active_input will be invalid.

CRs-Fixed: 1094825
Change-Id: I200ed352ff3c9d048884c9e464ba7d75fc7beeca