Update base sdk extension version to 1

S ships with extension version 1, so the correct base extension version
is 1 at the moment.

Bug: 199852423
Test: m out/host/linux-x86/development/sdk/platform_source.properties
      verify IsBaseSdk=true
Change-Id: I465d896fdeacfe34bdbfa0da1871d74a3bf3ee11