s390/pci: define isa_dma_bridge_buggy

Define isa_dma_bridge_buggy. Needed to make pci quirks compile:

drivers/pci/quirks.c: In function ‘quirk_isa_dma_hangs’:
drivers/pci/quirks.c:88:7: error: ‘isa_dma_bridge_buggy’ undeclared (first use in this function)

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