block/genhd: Change some numerals into macros

Rename the numerals in the diskstats_show() into the macros.

Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Liu Yuan <tailai.ly@taobao.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

block/genhd.c

@@ -1158,14 +1158,14 @@ static int diskstats_show(struct seq_file *seqf, void *v)
 			   "%u %lu %lu %llu %u %u %u %u\n",
 			   MAJOR(part_devt(hd)), MINOR(part_devt(hd)),
 			   disk_name(gp, hd->partno, buf),
-			   part_stat_read(hd, ios[0]),
-			   part_stat_read(hd, merges[0]),
-			   (unsigned long long)part_stat_read(hd, sectors[0]),
-			   jiffies_to_msecs(part_stat_read(hd, ticks[0])),
-			   part_stat_read(hd, ios[1]),
-			   part_stat_read(hd, merges[1]),
-			   (unsigned long long)part_stat_read(hd, sectors[1]),
-			   jiffies_to_msecs(part_stat_read(hd, ticks[1])),
+			   part_stat_read(hd, ios[READ]),
+			   part_stat_read(hd, merges[READ]),
+			   (unsigned long long)part_stat_read(hd, sectors[READ]),
+			   jiffies_to_msecs(part_stat_read(hd, ticks[READ])),
+			   part_stat_read(hd, ios[WRITE]),
+			   part_stat_read(hd, merges[WRITE]),
+			   (unsigned long long)part_stat_read(hd, sectors[WRITE]),
+			   jiffies_to_msecs(part_stat_read(hd, ticks[WRITE])),
 			   part_in_flight(hd),
 			   jiffies_to_msecs(part_stat_read(hd, io_ticks)),
 			   jiffies_to_msecs(part_stat_read(hd, time_in_queue))