s390/sclp: use LIST_HEAD for Initialization

For static initialization of list_head variable, use LIST_HEAD
instead of INIT_LIST_HEAD function.

Suggested-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Vineeth Vijayan <vneethv@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>