drm/amd/display: Fix incorrect end slope of EETF

Force the E2 to dc_fixpt_one when E1 exceeds that value. This is the
correct thing to do to avoid corruption.

Signed-off-by: SivapiriyanKumarasamy <sivapiriyan.kumarasamy@amd.com>
Reviewed-by: Krunoslav Kovac <Krunoslav.Kovac@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/modules/color/color_gamma.c

@@ -789,7 +789,8 @@ static void hermite_spline_eetf(struct fixed31_32 input_x,
 		// (t^3 - 2t^2 + t) * (1-ks)
 		E2 = dc_fixpt_add(E2, dc_fixpt_mul(temp2,
 				dc_fixpt_add(t, dc_fixpt_sub(t3, temp1))));
-	}
+	} else
+		E2 = dc_fixpt_one;
 
 	temp1 = dc_fixpt_sub(dc_fixpt_one, E2);
 	temp2 = dc_fixpt_mul(temp1, temp1);