Update submodule devices to latest Mon Sep 17 00:37:44 UTC 2018

    - devices in PX4/Firmware (8158cdfc): https://github.com/PX4/GpsDrivers/commit/aef48b04ff9b95350c4e5e507eea72a9e971d6a4
    - devices current upstream: https://github.com/PX4/GpsDrivers/commit/657514b26a0bf1b1ea2bf723b18449b04248822c
    - Changes: https://github.com/PX4/GpsDrivers/compare/aef48b04ff9b95350c4e5e507eea72a9e971d6a4...657514b26a0bf1b1ea2bf723b18449b04248822c

    657514b 2018-08-02 Alexis Paques - Adding UBX_MSG_RTCM3_* for additional messages
f9cf788 2018-08-02 Alexis Paques - Adding RTCM3 class documentation reference
6009a29 2018-08-02 Alexis Paques - Adding RTCM3 available output message IDs