s390/zfcp: use new address translation helpers

Use virt_to_dma64() and friends to properly convert virtual to physical and
physical to virtual addresses so that "make C=1" does not generate any
warnings anymore.

Reviewed-by: Steffen Maier <maier@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>