drm/amdgpu/pm: correct the firmware flag address for SMU IP v13.0.4

For SMU IP v13.0.4, the smnMP1_FIRMWARE_FLAGS address is different,
we need this to correct the reading address.

Signed-off-by: Tim Huang <tim.huang@amd.com>
Reviewed-by: Yifan Zhang <yifan1.zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>