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 a7c7bc4c0c47eaac77b8fa92f0672032df7f4254
Author: Rex Zhu <[email protected]>
Date:   Mon Mar 27 15:32:59 2017 +0800

    drm/amd/powerplay: reduce sample period time

    for power readings.

    Signed-off-by: Rex Zhu <[email protected]>
    Reviewed-by: Alex Deucher <[email protected]>
    Signed-off-by: Alex Deucher <[email protected]>
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 <[email protected]>
Acked-by: Alex Deucher <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>