dt-bindings: clock: rockchip: change SPDX-License-Identifier

Change SPDX-License-Identifier to (GPL-2.0+ OR MIT)
for Rockchip clock bindings.

Cc: Heiko Stübner <heiko@sntech.de>
Cc: Elaine Zhang <zhangqing@rock-chips.com>
Cc: Xing Zheng <zhengxing@rock-chips.com>
Cc: Jeffy Chen <jeffy.chen@rock-chips.com>
Cc: Finley Xiao <finley.xiao@rock-chips.com>
Cc: Andy Yan <andy.yan@rock-chips.com>
Cc: Shawn Lin <shawn.lin@rock-chips.com>
Cc: Eric Engestrom <eric@engestrom.ch>
Cc: Mylène Josserand <mylene.josserand@collabora.com>
Cc: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Acked-by: Eric Engestrom <eric@engestrom.ch>
Acked-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Link: https://lore.kernel.org/r/20c6a502-2ff5-bdb1-fb4f-0741f3a2c19c@gmail.com
[Rockchip Ack/request for dual licensing dt-bindings at
 https://lore.kernel.org/all/510d1180-bc8e-7820-c772-ed7f35447087@rock-chips.com/

]
Signed-off-by: Heiko Stuebner <heiko@sntech.de>