s390/ipl: Fix ipib handling for "dumpreipl" shutdown action

Fix problem that was introduced with patch "s390/smp: make absolute
lowcore / cpu restart parameter". After that patch the "dumpreipl"
shutdown action does not work any more. To fix the problem we have
to assign "reipl_block_actual" instead of "&reipl_block_actual"

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>