f2fs: change segment to section in f2fs_ioc_gc_range

f2fs_ioc_gc_range skips blocks_per_seg each time, however, f2fs_gc moves
blocks of section each time, so fix it from segment to section.
Signed-off-by: Yunlong Song <yunlong.song@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/file.c

@@ -2155,7 +2155,7 @@ static int f2fs_ioc_gc_range(struct file *filp, unsigned long arg)
 	}
 
 	ret = f2fs_gc(sbi, range.sync, true, GET_SEGNO(sbi, range.start));
-	range.start += sbi->blocks_per_seg;
+	range.start += BLKS_PER_SEC(sbi);
 	if (range.start <= end)
 		goto do_more;
 out: