dt-bindings: display: msm: qcm2290-mdss: Use the non-deprecated DSI compat

The "qcom,dsi-ctrl-6g-qcm2290" has been deprecated in
commit 0c0f65c6 ("dt-bindings: msm: dsi-controller-main: Add
compatible strings for every current SoC"), but the example hasn't been
updated to reflect that.

Fix that.

Fixes: 0c0f65c6

 ("dt-bindings: msm: dsi-controller-main: Add compatible strings for every current SoC")
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/569478/
Link: https://lore.kernel.org/r/20231125-topic-rb1_feat-v3-1-4cbb567743bb@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>