MIPS: X1000: Fix clock of watchdog node.

The devicetree ABI was broken on purpose by commit 6d532143
("watchdog: jz4740: Use regmap provided by TCU driver"), and
commit 1d9c3074 ("watchdog: jz4740: Use WDT clock provided
by TCU driver"). The commit message of the latter explains why the ABI
was broken.

However, the current devicetree files were not updated to the new ABI
described in Documentation/devicetree/bindings/timer/ingenic,tcu.txt,
so the watchdog driver would not probe.

Fix this problem by updating the clock of watchdog node from
"&cgu X1000_CLK_RTCLK" to "&tcu TCU_CLK_WDT" to comply with the new
ABI.

Fixes: 7a16ccd3 ("[v8,1/4] MIPS: Ingenic: Add Ingenic X1000 support.").
Signed-off-by: 周琰杰 (Zhou Yanjie) <zhouyanjie@wanyeetech.com>
Signed-off-by: Paul Burton <paulburton@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: devicetree@vger.kernel.org
Cc: paul@crapouillou.net
Cc: robh+dt@kernel.org
Cc: mark.rutland@arm.com
Cc: ralf@linux-mips.org
Cc: sernia.zhou@foxmail.com
Cc: zhenwenjin@gmail.com
Cc: dongsheng.qiu@ingenic.com