cifs: Fix memory leak on the deferred close

xfstests on smb21 report kmemleak as below:

  unreferenced object 0xffff8881767d6200 (size 64):
    comm "xfs_io", pid 1284, jiffies 4294777434 (age 20.789s)
    hex dump (first 32 bytes):
      80 5a d0 11 81 88 ff ff 78 8a aa 63 81 88 ff ff  .Z......x..c....
      00 71 99 76 81 88 ff ff 00 00 00 00 00 00 00 00  .q.v............
    backtrace:
      [<00000000ad04e6ea>] cifs_close+0x92/0x2c0
      [<0000000028b93c82>] __fput+0xff/0x3f0
      [<00000000d8116851>] task_work_run+0x85/0xc0
      [<0000000027e14f9e>] do_exit+0x5e5/0x1240
      [<00000000fb492b95>] do_group_exit+0x58/0xe0
      [<00000000129a32d9>] __x64_sys_exit_group+0x28/0x30
      [<00000000e3f7d8e9>] do_syscall_64+0x35/0x80
      [<00000000102e8a0b>] entry_SYSCALL_64_after_hwframe+0x46/0xb0

When cancel the deferred close work, we should also cleanup the struct
cifs_deferred_close.

Fixes: 9e992755 ("cifs: Call close synchronously during unlink/rename/lease break.")
Fixes: e3fc0656

 ("cifs: Deferred close performance improvements")
Cc: stable@vger.kernel.org
Reviewed-by: Shyam Prasad N <sprasad@microsoft.com>
Signed-off-by: Zhang Xiaoxu <zhangxiaoxu5@huawei.com>
Signed-off-by: Steve French <stfrench@microsoft.com>