Use uint64_t instead of size_t when calculating extent size to avoid overflow

Change-Id: I22a77162d08fd7e82ffaa3e0c6c8adb6e956f7d1
diff --git a/fs_mgr/liblp/super_layout_builder.cpp b/fs_mgr/liblp/super_layout_builder.cpp
index fd7416b..bff26ea 100644
--- a/fs_mgr/liblp/super_layout_builder.cpp
+++ b/fs_mgr/liblp/super_layout_builder.cpp
@@ -184,7 +184,7 @@
                 return {};
             }
 
-            size_t size = e.num_sectors * LP_SECTOR_SIZE;
+            uint64_t size = e.num_sectors * LP_SECTOR_SIZE;
             uint64_t super_offset = e.target_data * LP_SECTOR_SIZE;
             extents.emplace_back(super_offset, size, image_name, image_offset);