NULL pointer fixes

Hi,

The following commit landed in 6.4 that helps some occasional NULL pointer dereferences when setting up MST devices, particularly on suspend/resume cycles.

54d217406afe ("drm: use mgr->dev in drm_dbg_kms in drm_dp_add_payload_part2")

Can you please take this to 6.1.y and 6.3.y as well?  The NULL pointer de-reference has been reported on both.

Thanks,