Set sdk_version 28 in aidl_interface

default value of sdk_version in aidl_interface is changed.("28" -> "system_current")
so sdk_version of this module have to be "28" because it is included in framework.jar.

Test: m -j
Bug: 126469673
Change-Id: I515b1b236a7212198c419432b7c9fc70c623c63a