s390/appldata: restore missing init_virt_timer()

Commit 27f6b416 "s390/vtimer: rework virtual timer interface" removed
the call to init_virt_timer() by mistake, which is added again by this
patch.

Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>