drm/amdgpu/gfx9.4.3: Explicitly halt MEC before init

Need to make sure it's halted as we don't know what state
the GPU may have been left in previously.

Tested-by: Amber Lin <[e-mail]>
Acked-by: Amber Lin <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/amdgpu/gfx_v9_4_3.c

···
 		r = gfx_v9_4_3_xcc_cp_compute_load_microcode(adev, xcc_id);
 		if (r)
 			return r;
+	} else {
+		gfx_v9_4_3_xcc_cp_compute_enable(adev, false, xcc_id);
 	}
 
 	r = gfx_v9_4_3_xcc_kiq_resume(adev, xcc_id);