NFS: Fix a compile issue when !CONFIG_NFS_V4_1

The attempt to display the implementation ID needs to be conditional on
whether or not CONFIG_NFS_V4_1 is defined

Reported-by: Bryan Schumaker <Bryan.Schumaker@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>