dt-bindings: display/msm: qcom, sm8150-mdss: correct DSI PHY compatible

Qualcomm SM8150 MDSS comes with a bit different 7nm DSI PHY with its own
compatible.  DTS already use it:

  sa8155p-adp.dtb: display-subsystem@ae00000: phy@ae94400:compatible:0: 'qcom,dsi-phy-7nm' was expected

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Patchwork: https://patchwork.freedesktop.org/patch/567178/
Link: https://lore.kernel.org/r/20231111142017.51922-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>