s390/pci: Add missing virt_to_phys() for directed DIBV

In commit 4e4dc65a ("s390/pci: use phys_to_virt() for AIBVs/DIBVs")
the setting of dibv_addr was missed when adding virt_to_phys(). This
only affects systems with directed interrupt delivery enabled which are
not generally available.

Fixes: 4e4dc65a

 ("s390/pci: use phys_to_virt() for AIBVs/DIBVs")
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>