drm/amd/display: Fix inconsistent timestamp type

[WHY]
An unsigned int timestamp variable is assigned with an unsigned
long long value. Also, the assignment directly converts the
tick value to us without using built-in get elapsed time function.

[HOW]
Cast the assigned value correctly and also use built-in function
to get the timestamp in the unit we want.

v2: squash in 64 bit division fix
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Pavle Kotarac <Pavle.Kotarac@amd.com>
Signed-off-by: Angus Wang <Angus.Wang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/modules/freesync/freesync.c

@@ -1230,6 +1230,7 @@ void mod_freesync_handle_v_update(struct mod_freesync *mod_freesync,
 {
 	struct core_freesync *core_freesync = NULL;
 	unsigned int cur_timestamp_in_us;
+	unsigned long long cur_tick;
 
 	if ((mod_freesync == NULL) || (stream == NULL) || (in_out_vrr == NULL))
 		return;
@@ -1239,7 +1240,9 @@ void mod_freesync_handle_v_update(struct mod_freesync *mod_freesync,
 	if (in_out_vrr->supported == false)
 		return;
 
-	cur_timestamp_in_us = div_u64(dm_get_timestamp(core_freesync->dc->ctx), 10);
+	cur_tick = dm_get_timestamp(core_freesync->dc->ctx);
+	cur_timestamp_in_us = (unsigned int)
+			div_u64(dm_get_elapse_time_in_ns(core_freesync->dc->ctx, cur_tick, 0), 1000);
 
 	in_out_vrr->flip_interval.vsyncs_between_flip++;
 	in_out_vrr->flip_interval.v_update_timestamp_in_us = cur_timestamp_in_us;