drm/amd: check num of link levels when update pcie param

In SR-IOV environment, the value of pcie_table->num_of_link_levels will
be 0, and num_of_levels - 1 will cause array index out of bounds

Signed-off-by: Lin.Cao <lincao12@amd.com>
Acked-by: Jingwen Chen <Jingwen.Chen2@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>