dt-bindings: qcom: add another exception to the device naming rule

The 'qcom,dsi-ctrl-6g-qcm2290' compatibility string was added in the
commit ee1f0967 ("drm/msm/dsi: Add support for qcm2290 dsi
controller") in February 2022, but was not properly documented in the
bindings. Adding this compatibility string to
display/msm/dsi-controller-main.yaml caused a warning from
qcom-soc.yaml. Fix the warning by adding an exception to the mentioned
file.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221104132316.1028137-1-dmitry.baryshkov@linaro.org