Import jni_generator from root package

Soong is undergoing a transition to where only the
root package is added to the python path, not the
package of the entrypoint script. Update this usage
to match the new behavior.

Bug: 245583294
Test: Presubmits
Change-Id: I7c8245bfa6a4215823e3df7e8f1be8f70af51d40

Author: Colecf

Diff for: base/android/jni_generator/jni_registration_generator.py

@@ -14,7 +14,7 @@
 import string
 import sys
 
-import jni_generator
+import base.android.jni_generator.jni_generator as jni_generator
 from build.android.gyp.util import build_utils