f2fs: do not update REQ_TIME in case of error conditions

The REQ_TIME should be updated only in case of success cases
as followed at all other places in the file system.

Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>