drm/amdgpu: Revert "drm/amdgpu: getting fan speed pwm for vega10 properly"

This reverts commit 16fb4dca.

Unfortunately, that commit causes fan monitors can't be read and written
properly.

Fixes: 16fb4dca ("drm/amdgpu: getting fan speed pwm for vega10 properly")
Signed-off-by: Asher Song <Asher.Song@amd.com>
Reviewed-by: Guchun Chen <guchun.chen@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>