Update API of MapInfo from libunwindstack

Use accessors to for all the fields.

Test: build
Change-Id: I6ae458002e059ef2f9d73931cc68f2f698f85d7e
diff --git a/libc/malloc_debug/PointerData.cpp b/libc/malloc_debug/PointerData.cpp
index 4f81ff7..90c9136 100644
--- a/libc/malloc_debug/PointerData.cpp
+++ b/libc/malloc_debug/PointerData.cpp
@@ -588,8 +588,8 @@
       dprintf(fd, "  bt_info");
       for (const auto& frame : *info.backtrace_info) {
         dprintf(fd, " {");
-        if (frame.map_info != nullptr && !frame.map_info->name.empty()) {
-          dprintf(fd, "\"%s\"", frame.map_info->name.c_str());
+        if (frame.map_info != nullptr && !frame.map_info->name().empty()) {
+          dprintf(fd, "\"%s\"", frame.map_info->name().c_str());
         } else {
           dprintf(fd, "\"\"");
         }