Update submodule mavlink to latest Wed Jan 12 00:39:16 UTC 2022

    - mavlink in PX4/Firmware (8f6718d): mavlink/mavlink@75204ad
    - mavlink current upstream: mavlink/mavlink@fc3539e
    - Changes: mavlink/mavlink@75204ad...fc3539e

    fc3539e1 2022-01-10 Josh Henderson - ardupilotmega: Sync to ArduPilot downstream 10-JAN-2022 (#1777)
27395aa7 2022-01-06 Julian Oes - pymavlink: update submodule to latest master (#1776)
2180611b 2022-01-06 Hamish Willee - MAV_WINCH_STATUS_CLUTCH_ENGAGED: Winch clutch is engaged allowing motor to move freely
7c6f104f 2022-01-05 Jacob Dahl - Extend WINCH_STATUS_FLAG and WINCH_ACTION (#1766)
dcb44e75 2022-01-06 Hamish Willee - Delete unused cmake tree (#1760)
5b8bec5b 2022-01-05 Hamish Willee - common.xml: AUTOTUNE_AXIS_YAW - fix value to correct one for bitmask (#1767)