drm/test: drm_exec: fix memory leak on object prepare

drm/test: drm_exec: fix memory leak on object prepare

drm_exec_prepare_obj() and drm_exec_prepare_array() both reserve
dma-fence slots and hence a dma_resv_list without ever freeing it.

Make sure to call drm_gem_private_object_fini() for each GEM object
passed to drm_exec_prepare_obj()/drm_exec_prepare_array() throughout the
test to fix this up.

While at it, remove some trailing empty lines.

Fixes: 9710631cc8f3 ("drm: add drm_exec selftests v4")
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230809225034.8803-1-dakr@redhat.com
Signed-off-by: Christian König <christian.koenig@amd.com>