drm/radeon: use time_after(a,b) to replace "a>b"

time_after() deals with timer wrapping correctly.
Signed-off-by: Yu Zhe <yuzhe@nfschina.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_pm.c

@@ -1899,7 +1899,7 @@ static void radeon_dynpm_idle_work_handler(struct work_struct *work)
 		 * to false since we want to wait for vbl to avoid flicker.
 		 */
 		if (rdev->pm.dynpm_planned_action != DYNPM_ACTION_NONE &&
-		    jiffies > rdev->pm.dynpm_action_timeout) {
+		    time_after(jiffies, rdev->pm.dynpm_action_timeout)) {
 			radeon_pm_get_dynpm_state(rdev);
 			radeon_pm_set_clocks(rdev);
 		}