[submodules] updated to a new chibios repository

https://github.com/ChibiOS/ChibiOS-RT.git is not a valid repository anomore, the latest (stable) version of chibios (2.6.2) is available at https://github.com/ChibiOS/ChibiOS-gitmain.git

Hopefully it still works with the chibios code for data logging (master branch), rt_paparazzi currently uses a separate repository of ChibiOS (https://github.com/podhrmic/ChibiOS-RT.git, also version 2.6.2).