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 <wxt@rock-chips.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>