f2fs: fix normal discard process

f2fs: fix normal discard process

In the DPOLICY_BG mode, there is a conflict between
the two conditions "i + 1 < dpolicy->granularity" and
"i < DEFAULT_DISCARD_GRANULARITY". If i = 15, the first
condition is false, it will enter the second condition
and dispatch all small granularity discards in function
 __issue_discard_cmd_orderly. The restrictive effect
of the first condition to small discards will be
invalidated. These two conditions should align.

Fixes: 20ee4382322c ("f2fs: issue small discard by LBA order")
Signed-off-by: Dongdong Zhang <zhangdongdong1@oppo.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>