Fix jsc-android not found if building from source (#24547)

Summary:
If an app [builds from RN source](https://facebook.github.io/react-native/docs/building-from-source), there was an error for jsc-android not found.
It is a side effect of my previous [JSC as node dependency change](https://github.com/facebook/react-native/commit/8e375850de73d1b998a83279e6c4ba238867a453)
For building from RN source case, the jsc-android is located at `/path/to/app/node_modules/jsc-android`.
Original gradle task will try to find it at `/path/to/app/node_modules/react-native/ReactAndroid/../node_modules/jsc-android`, as ReactAndroid project path was being override inside node_modules.
The change fixes the building from source case.

N/A
This change does not need to publish into changelog, as it is a master branch building fix.
Pull Request resolved: https://github.com/facebook/react-native/pull/24547

Differential Revision: D15044703

Pulled By: cpojer

fbshipit-source-id: a7d824b1a14064d46c4a2ec9ea28255179174c83