nfs4: Fix kmemleak when allocate slot failed

If one of the slot allocate failed, should cleanup all the other
allocated slots, otherwise, the allocated slots will leak:

  unreferenced object 0xffff8881115aa100 (size 64):
    comm ""mount.nfs"", pid 679, jiffies 4294744957 (age 115.037s)
    hex dump (first 32 bytes):
      00 cc 19 73 81 88 ff ff 00 a0 5a 11 81 88 ff ff  ...s......Z.....
      00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    backtrace:
      [<000000007a4c434a>] nfs4_find_or_create_slot+0x8e/0x130
      [<000000005472a39c>] nfs4_realloc_slot_table+0x23f/0x270
      [<00000000cd8ca0eb>] nfs40_init_client+0x4a/0x90
      [<00000000128486db>] nfs4_init_client+0xce/0x270
      [<000000008d2cacad>] nfs4_set_client+0x1a2/0x2b0
      [<000000000e593b52>] nfs4_create_server+0x300/0x5f0
      [<00000000e4425dd2>] nfs4_try_get_tree+0x65/0x110
      [<00000000d3a6176f>] vfs_get_tree+0x41/0xf0
      [<0000000016b5ad4c>] path_mount+0x9b3/0xdd0
      [<00000000494cae71>] __x64_sys_mount+0x190/0x1d0
      [<000000005d56bdec>] do_syscall_64+0x35/0x80
      [<00000000687c9ae4>] entry_SYSCALL_64_after_hwframe+0x46/0xb0

Fixes: abf79bb3

 ("NFS: Add a slot table to struct nfs_client for NFSv4.0 transport blocking")
Signed-off-by: Zhang Xiaoxu <zhangxiaoxu5@huawei.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>