ARM: dts: qcom: replace gcc PXO with pxo_board fixed clock

Replace gcc PXO phandle to pxo_board fixed clock declared in the dts.
gcc driver doesn't provide PXO_SRC as it's a fixed-clock. This cause a
kernel panic if any driver actually try to use it.

Fixes: 40cf5c88 ("ARM: dts: qcom: add L2CC and RPM for IPQ8064")
Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220430055118.1947-2-ansuelsmth@gmail.com