ubifs: fix kernel-doc warnings

Fix kernel-doc warnings found when using "W=1".

file.c:1385: warning: Excess function parameter 'time' description in 'ubifs_update_time'
and 9 warnings like this one:
file.c:326: warning: No description found for return value of 'allocate_budget'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/oe-kbuild-all/202312030417.66c5PwHj-lkp@intel.com/
Cc: Richard Weinberger <richard@nod.at>
Cc: linux-mtd@lists.infradead.org
Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>
[rw: massaged patch to resolve conflict ]
Signed-off-by: Richard Weinberger <richard@nod.at>