iolog: Logging blocksize in IOPS traces

When saving bandwidth's with write_bw_log option, the last column
provides the blocksize used during the run.

When doing the same with write_io_log option, the last column was always
set to 0 which is confusing when reading the log file later.

This patch put both write_bw_log & write_io_log using the same semantic
by reporting the blocksize for every sample.
diff --git a/iolog.h b/iolog.h
index 7099097..8fedc19 100644
--- a/iolog.h
+++ b/iolog.h
@@ -118,7 +118,8 @@
 				unsigned int);
 extern void add_bw_sample(struct thread_data *, enum fio_ddir, unsigned int,
 				struct timeval *);
-extern void add_iops_sample(struct thread_data *, enum fio_ddir, struct timeval *);
+extern void add_iops_sample(struct thread_data *, enum fio_ddir, unsigned int,
+				struct timeval *);
 extern void init_disk_util(struct thread_data *);
 extern void update_rusage_stat(struct thread_data *);
 extern void setup_log(struct io_log **, unsigned long, int);