drm/amd/powerplay: remove redundant duplicated return check

The check on ret is duplicated in two places, it is redundant code.
Remove it.

Addresses-Coverity: ("Logically dead code")
Fixes: b94afb61 ("drm/amd/powerplay: honor hw limit on fetching metrics data for navi10")
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>