Fix kati --no_ignore_dirty usage

Kati only supports a single use of --no_ignore_dirty, so we were
ignoring the SOONG_ANDROID_MK file, and only detecting changes to
SOONG_MAKEVARS_MK. Fix this by using a pattern that should apply to both
of those makefiles.

Change-Id: I46390f9887f95f1db0efe4e93339667f35ebc67c