[SCSI] fix oops in all legacy host adapters caused by 6f381fa3

Commit 6f381fa3
Author: Lin Ming <ming.m.lin@intel.com>

[SCSI] scsi_lib: use correct DMA device in __scsi_alloc_queue
 
Caused a regression where we oops in every legacy mode SCSI host driver
because they supply a NULL pointer to scsi_add_host().  Fix this by checking
for the NULL in scsi_add_host_with_dma() and changing the DMA device to being
the platform_bus in that case (which replicates the original behaviour).
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

drivers/scsi/hosts.c

@@ -218,6 +218,9 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
 
 	if (!shost->shost_gendev.parent)
 		shost->shost_gendev.parent = dev ? dev : &platform_bus;
+	if (!dma_dev)
+		dma_dev = shost->shost_gendev.parent;
+
 	shost->dma_dev = dma_dev;
 
 	error = device_add(&shost->shost_gendev);