drm/amd/pm: correct the watermark settings for Polaris

The "/ 10" should be applied to the right-hand operand instead of
the left-hand one.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Noticed-by: Georgios Toptsidis <gtoptsid@gmail.com>
Reviewed-by: Feifei Xu <Feifei.Xu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org