progress.c: use dereferenced "progress" variable, not "(*p_progress)"

Since 98a1364740 (trace2: log progress time and throughput,
2020-05-12) stop_progress() dereferences a "struct progress **"
parameter in several places. Extract a dereferenced variable to reduce
clutter and make it clearer who needs to write to this parameter.

Now instead of using "*p_progress" several times in stop_progress() we
check it once for NULL and then use a dereferenced "progress" variable
thereafter. This uses the same pattern as the adjacent
stop_progress_msg() function, see ac900fddb7 (progress: don't
dereference before checking for NULL, 2020-08-10).

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

progress.c

@@ -319,21 +319,24 @@ static void finish_if_sparse(struct progress *progress)
 
 void stop_progress(struct progress **p_progress)
 {
+	struct progress *progress;
+
 	if (!p_progress)
 		BUG("don't provide NULL to stop_progress");
+	progress = *p_progress;
 
-	finish_if_sparse(*p_progress);
+	finish_if_sparse(progress);
 
-	if (*p_progress) {
+	if (progress) {
 		trace2_data_intmax("progress", the_repository, "total_objects",
-				   (*p_progress)->total);
+				   progress->total);
 
-		if ((*p_progress)->throughput)
+		if (progress->throughput)
 			trace2_data_intmax("progress", the_repository,
 					   "total_bytes",
-					   (*p_progress)->throughput->curr_total);
+					   progress->throughput->curr_total);
 
-		trace2_region_leave("progress", (*p_progress)->title, the_repository);
+		trace2_region_leave("progress", progress->title, the_repository);
 	}
 
 	stop_progress_msg(p_progress, _("done"));