drm/amd/display: Fix the delta clamping for shaper LUT

The shaper LUT requires a 10-bit value of the delta between segments. We
were using dc_fixpt_clamp_u0d10() to do that but it doesn't do what we
want it to do. It will preserve 10-bit precision after the decimal
point, but that's not quite what we want. We want 14-bit precision and
discard the 4 most-significant bytes.

To do that we'll do dc_fixpt_clamp_u0d14() & 0x3ff instead.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Krunoslav Kovac <krunoslav.kovac@amd.com>
Acked-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>