rockchip: clk: add watchdog clock to px30_clk_enable

Add the PCLK_WDT_NS clock to px30_clk_enable so that the watchdog driver
can probe since it wants to enable this clock.

Cc: Quentin Schulz <foss+uboot@0leil.net>
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>