pack-bitmap-write: use GIT_MAX_RAWSZ for allocation

Reviewed-by: Stefan Beller <sbeller@google.com>
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

pack-bitmap-write.c

@@ -37,7 +37,7 @@ struct bitmap_writer {
 
 	struct progress *progress;
 	int show_progress;
-	unsigned char pack_checksum[20];
+	unsigned char pack_checksum[GIT_MAX_RAWSZ];
 };
 
 static struct bitmap_writer writer;