drm/amd/powerplay: fix memory allocation failure check V2

Fix memory allocation failure check.

- V2: fix one more similar error

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