NFS: Fix potential race in nfs_fhget()

If we don't set the mode correctly in nfs_init_locked(), then there is
potential for a race with a second call to nfs_fhget that will cause
inode aliasing.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>