8.0 drm: Fix leak of damage blob id

This is more or less an automatic cherry-pick of the blob leak fix. We should carry it in 8.0 stable branch to avoid the following scenario:

• Someone adds FB_DAMAGE_CLIPS support into his kernel DRM driver. Someone else is using the driver with Weston and upgrades the kernel. Weston starts leaking kernel memory like mad and crashes the whole system. Bug gets reported to the kernel. The kernel developers fix it by taking atomic KMS away from all versions of Weston. Weston needs to be updated to re-enable atomic KMS.

This MR needs someone with the right drivers to test the fix still works.

cc @ascent