drm/amdgpu: Update amdgpu_device_indirect_r/wreg_ext

Only calculate pcie_index_hi for register address greater than 32bits.

Signed-off-by: Candice Li <candice.li@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>