ubifs: Fix some kernel-doc comments

Add description of @time and @flags in ubifs_update_time().

to silence the warnings:
fs/ubifs/file.c:1383: warning: Function parameter or member 'time' not described in 'ubifs_update_time'
fs/ubifs/file.c:1383: warning: Function parameter or member 'flags' not described in 'ubifs_update_time'

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Closes: https://bugzilla.openanolis.cn/show_bug.cgi?id=5848
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>