drm/amd/powerplay: bug fix for memory clock request from display

drm/amd/powerplay: bug fix for memory clock request from display

In some cases, display fixes memory clock frequency to a high value
rather than the natural memory clock switching.
When we comes back from s3 resume, the request from display is not reset,
this causes the bug which makes the memory clock goes into a low value.
Then due to the insuffcient memory clock, the screen flicks.

Signed-off-by: Kenneth Feng <kenneth.feng@amd.com>
Reviewed-by: Jack Xiao <Jack.Xiao@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>