s390/smp: sort out physical vs virtual pointers usage

With commit 57892847 ("s390/smp: reallocate IPL CPU lowcore")
virtual addresses are wrongly passed to memblock_free_late() and
SPX instructions on IPL CPU reinitialization.

Note: this does not fix a bug currently, since virtual and
physical addresses are identical.

Fixes: 57892847 ("s390/smp: reallocate IPL CPU lowcore")
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>