md: Simplify code with existing definition RESYNC_SECTORS in raid10.c

#define RESYNC_SECTORS (RESYNC_BLOCK_SIZE >> 9)

"RESYNC_BLOCK_SIZE/512" is equal to "RESYNC_BLOCK_SIZE >> 9", replace it
with RESYNC_SECTORS.
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Song Liu <songliubraving@fb.com>

drivers/md/raid10.c

@@ -4458,8 +4458,8 @@ static sector_t reshape_request(struct mddev *mddev, sector_t sector_nr,
 		last = conf->reshape_progress - 1;
 		sector_nr = last & ~(sector_t)(conf->geo.chunk_mask
 					       & conf->prev.chunk_mask);
-		if (sector_nr + RESYNC_BLOCK_SIZE/512 < last)
-			sector_nr = last + 1 - RESYNC_BLOCK_SIZE/512;
+		if (sector_nr + RESYNC_SECTORS < last)
+			sector_nr = last + 1 - RESYNC_SECTORS;
 	} else {
 		/* 'next' is after the last device address that we
 		 * might write to for this chunk in the new layout
@@ -4481,8 +4481,8 @@ static sector_t reshape_request(struct mddev *mddev, sector_t sector_nr,
 		last  = sector_nr | (conf->geo.chunk_mask
 				     & conf->prev.chunk_mask);
 
-		if (sector_nr + RESYNC_BLOCK_SIZE/512 <= last)
-			last = sector_nr + RESYNC_BLOCK_SIZE/512 - 1;
+		if (sector_nr + RESYNC_SECTORS <= last)
+			last = sector_nr + RESYNC_SECTORS - 1;
 	}
 
 	if (need_flush ||