thermal: rockchip: improve the warning log

It is no necessary to print warning agian and again if we don't
add rockchip,grf for dt, otherwise I saw the following log when
doing suspend-2-resume. We only need to print it once when parsing
dt. It looks quite trivial but the log is apparently verbose.

[ 26.615415] PM: early resume of devices complete after 1.539 msecs
[ 26.622002] rk_tsadcv2_initialize: Missing rockchip,grf property
[ 26.629359] rk_gmac-dwmac ff290000.ethernet: init for RGMII
[ 26.639794] PM: resume of devices complete after 18.109 msecs
[ 26.646925] Restarting tasks ... done.

Reviewed-by: Caesar Wang <[e-mail]>
Reviewed-by: Heiko Stuebner <[e-mail]>
Signed-off-by: Shawn Lin <[e-mail]>
Signed-off-by: Eduardo Valentin <[e-mail]>

drivers/thermal/rockchip_thermal.c

···
 		       regs + TSADCV2_AUTO_PERIOD_HT);
 	writel_relaxed(TSADCV2_HIGHT_TSHUT_DEBOUNCE_COUNT,
 		       regs + TSADCV2_HIGHT_TSHUT_DEBOUNCE);
-
-	if (IS_ERR(grf)) {
-		pr_warn("%s: Missing rockchip,grf property\n", __func__);
-		return;
-	}
 }
 
 /**
···
 	 * need this property.
 	 */
 	thermal->grf = syscon_regmap_lookup_by_phandle(np, "rockchip,grf");
+	if (IS_ERR(thermal->grf))
+		dev_warn(dev, "Missing rockchip,grf property\n");
 
 	return 0;
 }