drm/amd/powerplay: fix request smc_sk firmware case

This patch fixes firmware request error on polaris protection mode.
Because we need load smc_sk instead of smc under security protection
mode.

Signed-off-by: Huang Rui <ray.huang@amd.com>
Tested-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>