setuid/setuid04.c: Fix a double cleanup() error

The cleanup() may be called twice by both the parent and child process
in this testcase leading to a failure.

This patch makes sure cleanup() is called only once by parent process.

Signed-off-by: Zeng Linggang <zenglg.jy@cn.fujitsu.com>
Signed-off-by: Ma Shimiao <mashimiao.fnst@cn.fujitsu.com>
Reviewed-by: Cyril Hrubis <chrubis@suse.cz>