libnvdimm, btt: sparse fix

Fix:
drivers/nvdimm/btt.c:635:29: warning: restricted __le64 degrades to integer

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
diff --git a/drivers/nvdimm/btt.c b/drivers/nvdimm/btt.c
index 411c7b2..552f1c4 100644
--- a/drivers/nvdimm/btt.c
+++ b/drivers/nvdimm/btt.c
@@ -632,8 +632,9 @@
 	arena->logoff = arena_off + le64_to_cpu(super->logoff);
 	arena->info2off = arena_off + le64_to_cpu(super->info2off);
 
-	arena->size = (super->nextoff > 0) ? (le64_to_cpu(super->nextoff)) :
-			(arena->info2off - arena->infooff + BTT_PG_SIZE);
+	arena->size = (le64_to_cpu(super->nextoff) > 0)
+		? (le64_to_cpu(super->nextoff))
+		: (arena->info2off - arena->infooff + BTT_PG_SIZE);
 
 	arena->flags = le32_to_cpu(super->flags);
 }