drm/amdgpu: make BO type check less restrictive

BO with ttm_bo_type_sg type can also have tiling_flag and metadata.
So so BO type check for only ttm_bo_type_kernel.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Nirmoy Das <nirmoy.das@amd.com>
Reported-by: Tom StDenis <Tom.StDenis@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>