s390/pci: remove dead code

Get rid of these:

arch/s390/pci/pci_dma.c:16:29: warning: ‘zpci_ioat_dt’ defined but not used [-Wunused-variable]
arch/s390/pci/pci.c:164:12: warning: ‘zpci_store_fib’ defined but not used [-Wunused-function]

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>