[magma] Release device map atexit

Fixes a leak detected by asan only on Linux where dlclose affects the visibility of globals.

Run-All-Tests: true

Change-Id: I75ce3aa43947155c72872179eb4b6e14ee9e074d
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/mesa/+/693884
Reviewed-by: John Bauman <jbauman@google.com>
1 file changed