Compile fix:

fs/nfs/direct.c: In function 'nfs_get_user_pages':
fs/nfs/direct.c:110: warning: implicit declaration of function 'nfs_free_user_pages'
fs/nfs/direct.c: At top level:
fs/nfs/direct.c:127: warning: conflicting types for 'nfs_free_user_pages'
fs/nfs/direct.c:127: error: static declaration of 'nfs_free_user_pages' follows non-static declaration
fs/nfs/direct.c:110: error: previous implicit declaration of 'nfs_free_user_pages' was here

This should now be the same as fix that's going upstream.
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Acked-by: Trond Myklebust <trond.myklebust@fys.uio.no>