Fix crash in bindService due to uncleared binder identity

Clear the calling identity in retrieveServiceLocked before
doing the appop check. It probably needs to be cleared sooner
in general in retrieveServiceLocked(), but that might be a risky
fix. Making this smaller fix to keep it surgical for now.

Bug: 25759739
Change-Id: I66a5f8ef9b2d914181925fa344c3f2962030583d