s390/ipl: fix virtual vs physical address confusion

The value of ipl_cert_list_addr boot variable contains
a physical address, which is used directly. That works
because virtual and physical address spaces are currently
the same, but otherwise it is wrong.

While at it, fix also a comment for the platform keyring.

Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
Link: https://lore.kernel.org/r/20230816132942.2540411-1-agordeev@linux.ibm.com


Signed-off-by: Heiko Carstens <hca@linux.ibm.com>