drm: use mgr->dev in drm_dbg_kms in drm_dp_add_payload_part2

drm: use mgr->dev in drm_dbg_kms in drm_dp_add_payload_part2

Origin: https://git.kernel.org/linus/54d217406afe250d7a768783baaa79a035f21d38

I've been experiencing some intermittent crashes down in the display
driver code. The symptoms are ususally a line like this in dmesg:

    amdgpu 0000:30:00.0: [drm] Failed to create MST payload for port 000000006d3a3885: -5

...followed by an Oops due to a NULL pointer dereference.

Switch to using mgr->dev instead of state->dev since "state" can be
NULL in some cases.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=2184855
Suggested-by: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230419112447.18471-1-jlayton@kernel.org
Gbp-Pq: Topic bugfix/all
Gbp-Pq: Name drm-use-mgr-dev-in-drm_dbg_kms-in-drm_dp_add_payload.patch