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>

arch/s390/include/asm/dma.h

@@ -10,4 +10,10 @@
  */
 #define MAX_DMA_ADDRESS         0x80000000
 
+#ifdef CONFIG_PCI
+extern int isa_dma_bridge_buggy;
+#else
+#define isa_dma_bridge_buggy	(0)
+#endif
+
 #endif /* _ASM_S390_DMA_H */