drm/i915: fixup hangman rebase goof-up

I've added a bit of logic such that running the hangman test on chips
without any hw reset support at all doesn't wedge the gpu because the
reset failed. This relied on checking for non-null stop_rings.
Unfortunately I've botched a rebase somewhere and stop_rings is still
cleared at the old place before the reset code.

Fix this up so that running the i-g-t tests on gen2/3 doesn't result
in a wedged gpu.

v2: Actually remove the lines instead of adding them twice ... my git
license should be revoked immediately.

Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>