drm/i915: remember to call i915_sw_fence_fini

Seems to fix some object-debug splat which appeared while debugging
something unrelated.

v2: s/guc_blocked/guc_state.blocked/

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Tested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210924144646.4096402-1-matthew.auld@intel.com