Partially revert "drm/amd/display: Fix possible underflow for displays with large vblank"

This partially reverts commit de231189 ("drm/amd/display: Fix
possible underflow for displays with large vblank").

[Why]
The increased value of VBlankNomDefaultUS causes underflow at the
desktop of an IP KVM setup

[How]
Change the value from 800 back to 668
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Jun Lei <jun.lei@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Daniel Miess <daniel.miess@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dml/dcn314/dcn314_fpu.c

@@ -33,7 +33,7 @@
 #include "dml/display_mode_vba.h"
 
 struct _vcs_dpi_ip_params_st dcn3_14_ip = {
-	.VBlankNomDefaultUS = 800,
+	.VBlankNomDefaultUS = 668,
 	.gpuvm_enable = 1,
 	.gpuvm_max_page_table_levels = 1,
 	.hostvm_enable = 1,