If end_io gets an error, we don't need to set the page as dirty, since we
already set f2fs_stop_checkpoint which will not flush any data.

This will resolve the following warning.

======================================================
[ INFO: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected ]
4.4.0+ #9 Tainted: G           O
------------------------------------------------------
xfs_io/26773 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
 (&(&sbi->inode_lock[i])->rlock){+.+...}, at: [<ffffffffc025483f>] update_dirty_page+0x6f/0xd0 [f2fs]

and this task is already holding:
 (&(&q->__queue_lock)->rlock){-.-.-.}, at: [<ffffffff81396ea2>] blk_queue_bio+0x422/0x490
which would create a new lock dependency:
 (&(&q->__queue_lock)->rlock){-.-.-.} -> (&(&sbi->inode_lock[i])->rlock){+.+...}
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>