s390/kasan: sort out physical vs virtual memory confusion

s390/kasan: sort out physical vs virtual memory confusion

The kasan early boot memory allocators operate on pgalloc_pos
and segment_pos physical address pointers, but fail to convert
it to the corresponding virtual pointers.

Currently it is not a problem, since virtual and physical
addresses on s390 are the same. Nevertheless, should they
ever differ, this would cause an invalid pointer access.

Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>