arm64: dts: qcom: msm8998-mtp: correct board compatible

Add qcom,msm8998 SoC fallback to the board compatible.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220521164550.91115-12-krzysztof.kozlowski@linaro.org