drm/amd/pm: delete dead code

"ret" was checked earlier inside the loop, so we know it is zero here.
No need to check a second time.

Reviewed-by: Yang Wang <kevinyang.wang@amd.com>
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>