nfsd warning fix

gcc-4.3:

fs/nfsd/nfsctl.c: In function 'write_getfs':
fs/nfsd/nfsctl.c:248: warning: cast from pointer to integer of different size

Cc: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/nfsd/nfsctl.c

@@ -245,7 +245,7 @@ static ssize_t write_getfs(struct file *file, char *buf, size_t size)
 	}
 	exp_readunlock();
 	if (err == 0)
-		err = res->fh_size + (int)&((struct knfsd_fh*)0)->fh_base;
+		err = res->fh_size + offsetof(struct knfsd_fh, fh_base);
  out:
 	return err;
 }