drm/i915/selftests: Be explicit in ERR_PTR handling

When setting up a full GGTT, we expect the next insert to fail with
-ENOSPC. Simplify the use of ERR_PTR to not confuse either the reader or
smatch.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
References: f40a7b75 ("drm/i915: Initial selftests for exercising eviction")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191120093302.3723715-8-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/selftests/i915_gem_evict.c

@@ -198,8 +198,8 @@ static int igt_overcommit(void *arg)
 	quirk_add(obj, &objects);
 
 	vma = i915_gem_object_ggtt_pin(obj, NULL, 0, 0, 0);
-	if (!IS_ERR(vma) || PTR_ERR(vma) != -ENOSPC) {
-		pr_err("Failed to evict+insert, i915_gem_object_ggtt_pin returned err=%d\n", (int)PTR_ERR(vma));
+	if (vma != ERR_PTR(-ENOSPC)) {
+		pr_err("Failed to evict+insert, i915_gem_object_ggtt_pin returned err=%d\n", (int)PTR_ERR_OR_ZERO(vma));
 		err = -EINVAL;
 		goto cleanup;
 	}