Fix backwards compatible system property structure

The original structure included four reserved 32-bit values. This
change adds these back into the structure so that the
__system_property_find_compat function will (again) process the system
properties correctly.

libc/bionic/system_properties_compat.c

@@ -48,6 +48,7 @@ struct prop_area_compat {
     unsigned volatile serial;
     unsigned magic;
     unsigned version;
+    unsigned reserved[4];
     unsigned toc[1];
 };