dt-bindings: remoteproc: qcom: sc7180-pas: Fix SC7280 MPSS PD-names

The power domains for MPSS on SC7280 are actually named CX and MSS, and
not CX and MX. Adjust the name which also aligns the bindings with the
dts and fixes validation.

Fixes: 8bb92d6f

 ("dt-bindings: remoteproc: qcom,sc7180-pas: split into separate file")
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Luca Weiss <luca.weiss@fairphone.com>
Link: https://lore.kernel.org/r/20231208-sc7280-remoteprocs-v3-1-6aa394d33edf@fairphone.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>