drm/xe: Fix bo leak in xe_dma_buf_init_obj() on allocation failure

drm/xe: Fix bo leak in xe_dma_buf_init_obj() on allocation failure

When drm_gpuvm_resv_object_alloc() fails, the pre-allocated storage bo
is not freed. Add xe_bo_free(storage) before returning the error.

xe_dma_buf_init_obj() calls xe_bo_init_locked(), which frees the bo on
error. Therefore, xe_dma_buf_init_obj() must also free the bo on its own
error paths. Otherwise, since xe_gem_prime_import() cannot distinguish
whether the failure originated from xe_dma_buf_init_obj() or from
xe_bo_init_locked(), it cannot safely decide whether the bo should be
freed.

Add comments documenting the ownership semantics: on success, ownership
of storage is transferred to the returned drm_gem_object; on failure,
storage is freed before returning.

v2: Add comments to explain the free logic.

Fixes: eb289a5f6cc6 ("drm/xe: Convert xe_dma_buf.c for exhaustive eviction")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4.6
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260408175255.3402838-4-shuicheng.lin@intel.com
Signed-off-by: Shuicheng Lin <shuicheng.lin@intel.com>