drm/amdgpu: fix NULL pointer issue buffer funcs

[ Upstream commit 9877a86 ]

If SDMA block not enabled, buffer_funcs will not initialize,
fix the null pointer issue if buffer_funcs not initialized.

Signed-off-by: Likun Gao <Likun.Gao@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: Likun Gao

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

@@ -3280,7 +3280,8 @@ static int amdgpu_device_ip_init(struct amdgpu_device *adev)
 	if (r)
 		goto init_failed;
 
-	if (adev->mman.buffer_funcs_ring->sched.ready)
+	if (adev->mman.buffer_funcs_ring &&
+	    adev->mman.buffer_funcs_ring->sched.ready)
 		amdgpu_ttm_set_buffer_funcs_status(adev, true);
 
 	/* Don't init kfd if whole hive need to be reset during init */