drm/amd: Remove superfluous assignment for `adev->mes.adev`

`amdgpu_mes_init` already sets `adev->mes.adev`, so there is no need
to also set it in the IP specific versions.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>