mktemp: fix incorrect exit status from previous commit

* src/mktemp.c (main): Use an exit() strategy consistent with the
previous clauses dealing with optional error messages to ensure
we exit with the correct status in all cases.
Prompted by the continuous integration build failure at:
http://hydra.nixos.org/build/6412979

src/mktemp.c

@@ -335,7 +335,8 @@ main (int argc, char **argv)
           int saved_errno = errno;
           remove (dest_name);
           if (!suppress_file_err)
-            error (EXIT_FAILURE, saved_errno, _("write error"));
+            error (0, saved_errno, _("write error"));
+          status = EXIT_FAILURE;
         }
     }