NFS: Fix a compile glitch on 64-bit systems

fs/nfs/pagelist.c:226: error: conflicting types for 'nfs_pageio_init'
include/linux/nfs_page.h:80: error: previous declaration of 'nfs_pageio_init' was here

Thanks to Andrew for spotting this...

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