drm/amd/display: Fix increment when sampling OTF in DCE

Previously, the number of software segmets per region was reduced to 16.
This needs to be reflected in the sampling distance (increment) used when
translating to the hardware format.

Signed-off-by: Leo (Sunpeng) Li <sunpeng.li@amd.com>
Reviewed-by: Krunoslav Kovac <Krunoslav.Kovac@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>