Delete user data even on error when registering AccessorProviders

If ABinderRpc_registerAccessorProvider returns nullptr on error, we need
to make sure we still call the delete callback on the user data as the
user expects to be giving up ownership of it when they make the call.

Test: atest binderRpcTest
Bug: 358427181
Change-Id: I049e33f88ba202cd97e970276b50903374131eff