drm/i915/selftests: Fix some error codes

These error paths return success instead of negative error codes as
intended.

Fixes: c92724de ("drm/i915/selftests: Try to detect rollback during batchbuffer preemption")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/X/xMdcewtft7+QFM@mwanda

drivers/gpu/drm/i915/gt/selftest_execlists.c

@@ -3298,8 +3298,10 @@ static int live_preempt_user(void *arg)
 
 			rq = create_gpr_client(engine, global,
 					       NUM_GPR * i * sizeof(u32));
-			if (IS_ERR(rq))
+			if (IS_ERR(rq)) {
+				err = PTR_ERR(rq);
 				goto end_test;
+			}
 
 			client[i] = rq;
 		}