ubifs: describe function parameters

With 16a26b20

 ("ubifs: authentication: Add hashes to index nodes")
insert_node() and insert_dent() got a new function parameter 'hash'. Add
a description for this new parameter.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202311051618.D7YUE1Rr-lkp@intel.com/


Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>