drm/i915: Always call i915_gem_reset_finish() following i915_gem_reset_prepare()

As i915_gem_reset_finish() undoes the steps from
i915_gem_reset_prepare() to leave the system in a fully-working state,
e.g. to be able to free the breadcrumb signal threads, make sure that we
always call it even on the error path.

Fixes: da9a796f

 ("drm/i915: Split GEM resetting into 3 phases")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170212172002.23072-2-chris@chris-wilson.co.uk


Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
(cherry picked from commit 8d613c53

)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>