linker.h: don't change the soinfo structure

In 48527c3f740a80b45acb5a6efc217f771ae50143, we modified the soinfo
structure to remove an unnecessary variable. However, third party
programs seem to be relying on the structure not changing.
Add a dummy variable back into place to preserve structure.

Bug: 5064106

Change-Id: I3014dda1a46e624644b09e156c3e9381ba3729bd
1 file changed