CMake: fix value api_version in Core.json

Amends 8d2d556.

Core.json was using the older name variable name
QT_ANDROID_API_VERSION instead of the new name
QT_ANDROID_API_USED_FOR_JAVA.

Change-Id: I1c995818331f45eedb07114276b6aba0f6577c15
Reviewed-by: Shyamnath Premnadh <Shyamnath.Premnadh@qt.io>

cmake/QtModuleHelpers.cmake

@@ -1248,7 +1248,7 @@ function(qt_describe_module target)
     if(ANDROID)
         string(APPEND extra_build_information "
         \"android\": {
-            \"api_version\": \"${QT_ANDROID_API_VERSION}\",
+            \"api_version\": \"${QT_ANDROID_API_USED_FOR_JAVA}\",
             \"ndk\": {
                 \"version\": \"${ANDROID_NDK_REVISION}\"
             }