drm/i915/selftest: Fix potential memory leak

drm/i915/selftest: Fix potential memory leak

Object out is not released on path that no VMA instance found. The root
cause is jumping to an unexpected label on the error path.

Fixes: a47e788c2310 ("drm/i915/selftests: Exercise CS TLB invalidation")
Signed-off-by: Pan Bian <bianpan2016@163.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20210122015640.16002-1-bianpan2016@163.com
(cherry picked from commit 2b015017d5cb01477a79ca184ac25c247d664568)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>