'whiteout_ui->data' will be freed twice if space budget fail for
rename whiteout operation as following process:

rename_whiteout
  dev = kmalloc
  whiteout_ui->data = dev
  kfree(whiteout_ui->data)  // Free first time
  iput(whiteout)
    ubifs_free_inode
      kfree(ui->data)	    // Double free!

KASAN reports:
==================================================================
BUG: KASAN: double-free or invalid-free in ubifs_free_inode+0x4f/0x70
Call Trace:
  kfree+0x117/0x490
  ubifs_free_inode+0x4f/0x70 [ubifs]
  i_callback+0x30/0x60
  rcu_do_batch+0x366/0xac0
  __do_softirq+0x133/0x57f

Allocated by task 1506:
  kmem_cache_alloc_trace+0x3c2/0x7a0
  do_rename+0x9b7/0x1150 [ubifs]
  ubifs_rename+0x106/0x1f0 [ubifs]
  do_syscall_64+0x35/0x80

Freed by task 1506:
  kfree+0x117/0x490
  do_rename.cold+0x53/0x8a [ubifs]
  ubifs_rename+0x106/0x1f0 [ubifs]
  do_syscall_64+0x35/0x80

The buggy address belongs to the object at ffff88810238bed8 which
belongs to the cache kmalloc-8 of size 8
==================================================================

Let ubifs_free_inode() free 'whiteout_ui->data'. BTW, delete unused
assignment 'whiteout_ui->data_len = 0', process 'ubifs_evict_inode()
-> ubifs_jnl_delete_inode() -> ubifs_jnl_write_inode()' doesn't need it
(because 'inc_nlink(whiteout)' won't be excuted by 'goto out_release',
 and the nlink of whiteout inode is 0).

Fixes: 9e0a1fff ("ubifs: Implement RENAME_WHITEOUT")
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>