watchdog: starfive: Add missing clk_disable_unprepare()

Add the missing clk_disable_unprepare() before return in
starfive_wdt_enable_clock().

Signed-off-by: Chen Ni <nichen@iscas.ac.cn>
Reviewed-by: Xingyu Wu <xingyu.wu@starfivetech.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20240628033508.281058-1-nichen@iscas.ac.cn


Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>