arm64: dts: cavium: thunder2-99xx: drop redundant reg-names

arm64: dts: cavium: thunder2-99xx: drop redundant reg-names

There is no "reg-names" property in the PCI bindings and the value does
not conform to Devicetree coding style (upper-case letters, space), so
assume this was copied from downstream.

This fixes dtbs_check warning:

  thunder2-99xx.dtb: pcie@30000000: Unevaluated properties are not allowed ('reg-names' was unexpected)

Link: https://lore.kernel.org/r/20240407102841.38617-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>