NFS: Re-enable compilation of nfs with !CONFIG_NFS_V4 || !CONFIG_NFS_V4_1

Fix two recently introduced compile problems:

Fix a typo in fs/nfs/pnfs.h

Move the pnfs_blksize declaration outside the CONFIG_NFS_V4 section in
struct nfs_server.

Reported-by: Jens Axboe <jaxboe@fusionio.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>