commit-graph.c: display correct number of chunks when writing

When writing a commit-graph, a progress meter is shown which indicates
the number of pieces of data to write (one per commit in each chunk).

In 47410aa (commit-graph: use chunk-format write API, 2021-02-18),
the number of chunks became tracked by the new chunk-format API. But a
stray local variable was left behind from when write_commit_graph_file()
used to keep track of the same.

Since this was no longer updated after 47410aa, the progress meter
appeared broken:

    $ git commit-graph write --reachable
    Expanding reachable commits in commit graph: 837569, done.
    Writing out commit graph in 3 passes: 166% (4187845/2512707), done.

Drop the local variable and rely instead on the chunk-format API to tell
us the correct number of chunks.

Reported-by: SZEDER Gábor <[email protected]>
Signed-off-by: Taylor Blau <[email protected]>
Acked-by: Derrick Stolee <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

commit-graph.c

@@ -1715,7 +1715,6 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 	struct lock_file lk = LOCK_INIT;
 	const unsigned hashsz = the_hash_algo->rawsz;
 	struct strbuf progress_title = STRBUF_INIT;
-	int num_chunks = 3;
 	struct object_id file_hash;
 	struct chunkfile *cf;
 
@@ -1811,11 +1810,11 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 		strbuf_addf(&progress_title,
 			    Q_("Writing out commit graph in %d pass",
 			       "Writing out commit graph in %d passes",
-			       num_chunks),
-			    num_chunks);
+			       get_num_chunks(cf)),
+			    get_num_chunks(cf));
 		ctx->progress = start_delayed_progress(
 			progress_title.buf,
-			num_chunks * ctx->commits.nr);
+			get_num_chunks(cf) * ctx->commits.nr);
 	}
 
 	write_chunkfile(cf, ctx);