nfs4: fix a typo of NFS_ATTR_FATTR_GROUP_NAME

nfs4: fix a typo of NFS_ATTR_FATTR_GROUP_NAME

This typo cause a memory leak, and a bad client's group id.
unreferenced object 0xffff96d8073998d0 (size 8):
  comm "kworker/0:3", pid 34224, jiffies 4295361338 (age 761.752s)
  hex dump (first 8 bytes):
    30 00 39 07 d8 96 ff ff                          0.9.....
  backtrace:
    [<ffffffffb883212a>] kmemleak_alloc+0x4a/0xa0
    [<ffffffffb8237bc0>] __kmalloc+0x140/0x220
    [<ffffffffc05c921c>] xdr_stream_decode_string_dup+0x7c/0x110 [sunrpc]
    [<ffffffffc08edcf0>] decode_getfattr_attrs+0x940/0x1630 [nfsv4]
    [<ffffffffc08eea7b>] decode_getfattr_generic.constprop.108+0x9b/0x100 [nfsv4]
    [<ffffffffc08eebaf>] nfs4_xdr_dec_open+0xcf/0x100 [nfsv4]
    [<ffffffffc05bf9c7>] rpcauth_unwrap_resp+0xa7/0xe0 [sunrpc]
    [<ffffffffc05afc70>] call_decode+0x1e0/0x810 [sunrpc]
    [<ffffffffc05bc64d>] __rpc_execute+0x8d/0x420 [sunrpc]
    [<ffffffffc05bc9f2>] rpc_async_schedule+0x12/0x20 [sunrpc]
    [<ffffffffb80bb077>] process_one_work+0x197/0x430
    [<ffffffffb80bb35e>] worker_thread+0x4e/0x4a0
    [<ffffffffb80c1d41>] kthread+0x101/0x140
    [<ffffffffb8839a5c>] ret_from_fork+0x2c/0x40
    [<ffffffffffffffff>] 0xffffffffffffffff

Fixes: 686a816ab6 ("NFSv4: Clean up owner/group attribute decode")
Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>