drm/amd/pm: fix pcie information for sienna cichlid

Fix the function used for sienna cichlid to get correct PCIE information
by pp_dpm_pcie.

Signed-off-by: Likun Gao <Likun.Gao@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Kenneth Feng <kenneth.feng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>