drm/i915/selftests: Unwind hugepages to drop wakeref on error

Make sure that upon error after we have acquired the wakeref we do
release it again.

v2: add another missing "goto out_wf"(Andi).

Fixes: 027c38b4 ("drm/i915/selftests: Grab the runtime pm in shrink_thp")
Cc: Andi Shyti <andi.shyti@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Signed-off-by: Chris Wilson <chris.p.wilson@linux.intel.com>
Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230117123234.26487-1-nirmoy.das@intel.com