NFS: Don't trace an uninitialised value

If fhandle is NULL or fattr is NULL, then 'error' is uninitialised.
Reported-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>

fs/nfs/dir.c

@@ -1814,7 +1814,7 @@ struct dentry *nfs_lookup(struct inode *dir, struct dentry * dentry, unsigned in
 	}
 	nfs_set_verifier(dentry, dir_verifier);
 out_label:
-	trace_nfs_lookup_exit(dir, dentry, flags, error);
+	trace_nfs_lookup_exit(dir, dentry, flags, PTR_ERR_OR_ZERO(res));
 	nfs4_label_free(label);
 out:
 	nfs_free_fattr(fattr);