platform: starfive: correct system clock device tree node

Starfive names the system clock device tree node "starfive,jh7110-clkgen"
in all their git repositories. However, a different name is used in
upstream U-Boot (and also Linux): "starfive,jh7110-syscrg". Since
OpenSBI gets the device tree from U-Boot, this inconsistency leads the
problem that OpenSBI doesn't know the system clock device exists.

Correct this name to keep the consistency.

Signed-off-by: Nam Cao <namcao@linutronix.de>
Acked-by: Minda Chen <minda.chen@starfivetech.com>
Tested-by: Minda Chen <minda.chen@starfivetech.com>
Reviewed-by: Anup Patel <anup@brainfault.org>