libnvdimm, region: update nd_region_available_dpa() for multi-pmem support

The free dpa (dimm-physical-address) space calculation reports how much
free space is available with consideration for aliased BLK + PMEM
regions.  Recall that BLK capacity is allocated from high addresses and
PMEM is allocated from low addresses in their respective regions.

nd_region_available_dpa() accounts for the fact that the largest
encroachment (lowest starting address) into PMEM capacity by a BLK
allocation limits the available capacity to that point, regardless if
there is BLK allocation hole at a higher address.  Similarly, for the
multi-pmem case we need to track the largest encroachment (highest
 ending address) of a PMEM allocation in BLK capacity regardless of
whether there is an allocation hole that a BLK allocation could fill at
a lower address.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/nvdimm/region_devs.c

@@ -294,9 +294,8 @@ resource_size_t nd_region_available_dpa(struct nd_region *nd_region)
 				blk_max_overlap = overlap;
 				goto retry;
 			}
-		} else if (is_nd_blk(&nd_region->dev)) {
-			available += nd_blk_available_dpa(nd_mapping);
-		}
+		} else if (is_nd_blk(&nd_region->dev))
+			available += nd_blk_available_dpa(nd_region);
 	}
 
 	return available;