arm64: dts: qcom: sc7280: assign DSI clock source parents

Assign DSI clock source parents to DSI PHY clocks.

Signed-off-by: Rajeev Nandan <quic_rajeevny@quicinc.com>
Cc: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/1662550553-28933-1-git-send-email-quic_rajeevny@quicinc.com