[lavapipe] Fix memory leak (lvp_device).

- Also fixed no-op assignments to zero.

Change-Id: I5208dd2b8f00a2f314dc761a34da7fb9736d8547
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/mesa/+/1129690
Commit-Queue: John Rosasco <rosasco@google.com>
Fuchsia-Auto-Submit: John Rosasco <rosasco@google.com>
Reviewed-by: Josh Gargus <jjosh@google.com>