drm/mst: Fix up u64 division

Change rem_nsec to u32 since that's what do_div returns, this avoids the
u64 divide in the drm_print args.

Changes in v2:
- Instead of doing do_div in drm_print, make rem_nsec u32 (Ville)

Link to v1: https://patchwork.freedesktop.org/patch/msgid/20191106173622.15573-1-sean@poorly.run

Fixes: 12a280c7 ("drm/dp_mst: Add topology ref history tracking for debugging")
Cc: Juston Li <juston.li@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Harry Wentland <hwentlan@amd.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sean Paul <sean@poorly.run>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191106194121.164458-1-sean@poorly.run

drivers/gpu/drm/drm_dp_mst_topology.c

@@ -1507,12 +1507,12 @@ __dump_topology_ref_history(struct drm_dp_mst_topology_ref_history *history,
 		ulong *entries;
 		uint nr_entries;
 		u64 ts_nsec = entry->ts_nsec;
-		u64 rem_nsec = do_div(ts_nsec, 1000000000);
+		u32 rem_nsec = do_div(ts_nsec, 1000000000);
 
 		nr_entries = stack_depot_fetch(entry->backtrace, &entries);
 		stack_trace_snprint(buf, PAGE_SIZE, entries, nr_entries, 4);
 
-		drm_printf(&p, "  %d %ss (last at %5llu.%06llu):\n%s",
+		drm_printf(&p, "  %d %ss (last at %5llu.%06u):\n%s",
 			   entry->count,
 			   topology_ref_type_to_str(entry->type),
 			   ts_nsec, rem_nsec / 1000, buf);