Fix memory-leak on soinfo_free()

Bug: http://b/22290728
Change-Id: I00747056db2cd3ff8b33936278464daed7236536
(cherry picked from commit 609f11b31ecedc4e9f2a1f6017b60b1f51b15c22)
diff --git a/linker/linker.cpp b/linker/linker.cpp
index 60f8489..e84036a 100644
--- a/linker/linker.cpp
+++ b/linker/linker.cpp
@@ -277,6 +277,7 @@
     sonext = prev;
   }
 
+  si->~soinfo();
   g_soinfo_allocator.free(si);
 }