dax: fix mapping size check

pgoff_to_phys() validates that both the starting address and the length
of the mapping against the resource list.  We need to check for a
mapping size of PMD_SIZE not PAGE_SIZE in the pmd fault path.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

drivers/dax/dax.c

@@ -459,7 +459,7 @@ static int __dax_dev_pmd_fault(struct dax_dev *dax_dev,
 	}
 
 	pgoff = linear_page_index(vma, pmd_addr);
-	phys = pgoff_to_phys(dax_dev, pgoff, PAGE_SIZE);
+	phys = pgoff_to_phys(dax_dev, pgoff, PMD_SIZE);
 	if (phys == -1) {
 		dev_dbg(dev, "%s: phys_to_pgoff(%#lx) failed\n", __func__,
 				pgoff);