drm/i915/gem: Check the correct variable in selftest

There is a copy and paste bug in this code.  It's supposed to check
"obj2" instead of checking "obj" a second time.

Fixes: 80f0b679

 ("drm/i915: Add an implementation for i915_gem_ww_ctx locking, v2.")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Andi Shyti <andi.shyti@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/8ilneOcJAjwqU4t@mwand