rust: drm: gem: clean up GEM state in init failure case

rust: drm: gem: clean up GEM state in init failure case

Currently, if `drm_gem_object_init` fails, the object is freed without
any cleanup. Perform the cleanup in that case.

Cc: stable@vger.kernel.org
Fixes: c284d3e42338 ("rust: drm: gem: Add GEM object abstraction")
Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Onur Özkan <work@onurozkan.dev>
Link: https://patch.msgid.link/20260423-fix-gem-1-v1-1-e12e35f7bba9@nvidia.com
[ Move safety comment closer to unsafe block to avoid a clippy warning.
  - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>