nilfs2: add missing argument descriptions for ioctl-related helpers

nilfs2: add missing argument descriptions for ioctl-related helpers

Add missing argument descriptions and return value information to the
kernel-doc comments for ioctl helper functions, and eliminate the
following warnings output by the kernel-doc script:

 fs/nilfs2/ioctl.c:120: warning: Function parameter or struct member
  'dentry' not described in 'nilfs_fileattr_get'
 fs/nilfs2/ioctl.c:120: warning: Function parameter or struct member 'fa'
  not described in 'nilfs_fileattr_get'
 fs/nilfs2/ioctl.c:133: warning: Function parameter or struct member 'idmap'
  not described in 'nilfs_fileattr_set'
 fs/nilfs2/ioctl.c:133: warning: Function parameter or struct member
  'dentry' not described in 'nilfs_fileattr_set'
 fs/nilfs2/ioctl.c:133: warning: Function parameter or struct member 'fa'
  not described in 'nilfs_fileattr_set'
 fs/nilfs2/ioctl.c:164: warning: Function parameter or struct member 'inode'
  not described in 'nilfs_ioctl_getversion'
 fs/nilfs2/ioctl.c:164: warning: Function parameter or struct member 'argp'
  not described in 'nilfs_ioctl_getversion'

Link: https://lkml.kernel.org/r/20240816074319.3253-3-konishi.ryusuke@gmail.com
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>