Fixed a wrong AIDL import path

AIDL import path should point to a root directory where relative path to
an AIDL file encodes the fully qualified name of the type in the file.

Since libvold_binder imports types like
android.os.incremental.IncrementalFileSystemControlParcel which are
under frameworks/base/core/java, the import path should set to the path,
not to the sub directory that directly has the AIDL files.

Bug: 147918827
Test: m
Change-Id: Ic4941578813eced5a7eb59a0656c10b76e902515