NFS/flexfiles: Use the correct TCP timeout for flexfiles I/O

Fix a typo where we're confusing the default TCP retrans value
(NFS_DEF_TCP_RETRANS) for the default TCP timeout value.

Fixes: 15d03055

 ("pNFS/flexfiles: Set reasonable default ...")
Cc: stable@vger.kernel.org # 4.8+
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>