NFS: Cleanup - only store the write verifier in struct nfs_page

The 'committed' field is not needed once we have put the struct nfs_page
on the right list.

Also correct the type of the verifier: it is not an array of __be32, but
simply an 8 byte long opaque array.

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

include/linux/nfs_page.h

@@ -42,7 +42,7 @@ struct nfs_page {
 				wb_bytes;	/* Length of request */
 	struct kref		wb_kref;	/* reference count */
 	unsigned long		wb_flags;
-	struct nfs_writeverf	wb_verf;	/* Commit cookie */
+	struct nfs_write_verifier	wb_verf;	/* Commit cookie */
 };
 
 struct nfs_pageio_descriptor;