Fix Android Makefile relative paths

[aarongrider]

Relative make paths were incorrect and causing an Android build error. Updated that to have the correct relative path.

`* What went wrong:
Execution failed for task ':react-native-mmkv:generateJsonModelDebug'.

/Users//Developer//node_modules/react-native-mmkv/android/CMakeLists.txt : C/C++ debug|armeabi-v7a : CMake Error at /Users//Developer//node_modules/react-native-mmkv/android/CMakeLists.txt:15 (add_library):
Cannot find source file:

  ../node_modules/react-native/ReactCommon/jsi/jsi/jsi.cpp

Tried extensions .c .C .c++ .cc .cpp .cxx .m .M .mm .h .hh .h++ .hm .hpp
.hxx .in .txx

• Try:
  Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

• Get more help at https://help.gradle.org

BUILD FAILED in 15s`

[KingAmo]

#4 i just run into this issue

update: i have tried this pr, and it works for me, thanks!

[mrousavy]

Thanks for your PR! ❤️

I will not merge this right now though since I'm trying to build with android .aar so that users don't need to install NDK and build the project for themselves.

[mrousavy]

Pre-built .aar package will be used in v0.1.11.