pmem, dax: disable dax in the presence of bad blocks

Longer term teach dax to punch "error" holes in mapping requests and
deliver SIGBUS to applications that consume a bad pmem page.  For now,
simply disable the dax performance optimization in the presence of known
errors.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index d00c659..6a1832b 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -233,6 +233,7 @@
 		return -ENOMEM;
 	nvdimm_namespace_add_poison(ndns, &pmem->bb, pmem->data_offset);
 
+	disk->bb = &pmem->bb;
 	add_disk(disk);
 	revalidate_disk(disk);