s390/kexec_file: fix initrd location for kdump kernel

commit 70b69054 upstream.

initrd_start must not point at the location the initrd is loaded into
the crashkernel memory but at the location it will be after the
crashkernel memory is swapped with the memory at 0.

Fixes: ee337f54

 ("s390/kexec_file: Add crash support to image loader")
Reported-by: Lianbo Jiang <lijiang@redhat.com>
Signed-off-by: Philipp Rudo <prudo@linux.ibm.com>
Tested-by: Lianbo Jiang <lijiang@redhat.com>
Link: https://lore.kernel.org/r/20200512193956.15ae3f23@laptop2-ibm.local
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>