Tweak comments for OpenJDK 9 build toolchain logic.

This addresses review comments on the preceding CL
http://r.android.com/539055

Test: Treehugger
Change-Id: Icb0674190db3d638546a0ed49dbcb97d0698e549
diff --git a/core/config.mk b/core/config.mk
index debe918..05fb926 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -686,7 +686,7 @@
 # http://b/38418220
 ifndef USE_OPENJDK9
 HOST_JDK_TOOLS_JAR := $(ANDROID_JAVA_TOOLCHAIN)/../lib/tools.jar
-endif # ifdef USE_OPENJDK9
+endif # ifndef USE_OPENJDK9
 
 # It's called md5 on Mac OS and md5sum on Linux
 ifeq ($(HOST_OS),darwin)