s390/diag: handle diag 204 subcode 4 address correctly

Diagnose 204 subcode 4 requires a real (physical) address, but a
virtual address is passed to the inline assembly.

Convert the address to a physical address for only this specific case.

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