Fix lint warnings in LatinIME JNI code

This CL addresses compiler warnings when building libjni_latinime.so
with NDK from Android Studio.

There should be no behavior change.

Bug: 110741422
Bug: 110757803
Test: tapas LatinIME LatinIMETests arm64 userdebug && make -j
Change-Id: Icc711dd46511a167b1fd90028552def5b2f9941f