arm64: dts: broadcom: Fix SP805 clock-names

The SP805 binding sets the name for the actual watchdog clock to
"wdog_clk" (with an underscore).

Change the name in the DTs for Broadcom platforms to match that. The
Linux and U-Boot driver use the *first* clock for this purpose anyway,
so it does not break anything.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Ray Jui <ray.jui@broadcom.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>