drm/i915/selftests: Change priority overflow detection

Check for integer overflow in the priority chain, rather than against a
type-constricted max-priority check.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200519063123.20673-2-chris@chris-wilson.co.uk

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

@@ -2735,12 +2735,12 @@ static int live_preempt_gang(void *arg)
 			/* Submit each spinner at increasing priority */
 			engine->schedule(rq, &attr);
 
+			if (prio < attr.priority)
+				break;
+
 			if (prio <= I915_PRIORITY_MAX)
 				continue;
 
-			if (prio > (INT_MAX >> I915_USER_PRIORITY_SHIFT))
-				break;
-
 			if (__igt_timeout(end_time, NULL))
 				break;
 		} while (1);