drm/amd/powerply: fix power reading on Fiji

drm/amd/powerply: fix power reading on Fiji

Power value is wrong reported by customer. It is a regression by

commit dd349aeff1101cb0a17e3c7f2602f739c978b018
Author: Rex Zhu <Rex.Zhu@amd.com>
Date:   Mon Mar 27 15:32:59 2017 +0800

    drm/amd/powerplay: reduce sample period time

    for power readings.

    Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
    Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
    Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
The theoretical sampling period is from 50ms to 4sec, original 2sec
is long but correct, and 20ms is too short. change it to more
reasonable 200ms.

Signed-off-by: Eric Huang <JinHuiEric.Huang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>