arm64: dts: hisilicon: fix arm,sp805 compatible string

[ Upstream commit 894d4f1f77d0e88f1f81af2e1e37333c1c41b631 ]

According to Documentation/devicetree/bindings/watchdog/arm,sp805.yaml
the compatible is:
  compatible = "arm,sp805", "arm,primecell";

The current compatible string doesn't exist at all. Fix it.

Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>