busybox: fix upgrade path

 * check_data_file_clashes: Package busybox-syslog wants to install file /lib/systemd/system/busybox-syslog.service
        But that file is already provided by package  * busybox-syslog-systemd
 * check_data_file_clashes: Package busybox-syslog wants to install file /lib/systemd/system/syslog.service
        But that file is already provided by package  * busybox-syslog-systemd
 * check_data_file_clashes: Package busybox-syslog wants to install file /lib/systemd/system/busybox-klogd.service
        But that file is already provided by package  * busybox-syslog-systemd

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>