qualcommax: ipq50xx: fix XO board clock rate for Yuncore AX850

qualcommax: ipq50xx: fix XO board clock rate for Yuncore AX850

Commit 468975a985ab changed the XO board clock definition from a fixed
clock to a fixed rate clock in the dtsi.

As such, boards must use clock dividers and multipliers to calculate
the clock rate based on the referenced parent clock.

Fixes: 5d2994a73e20 ("qualcommax: ipq50xx: Add support for Yuncore AX850")
Signed-off-by: George Moussalem <george.moussalem@outlook.com>
Link: https://github.com/openwrt/openwrt/pull/20405
Signed-off-by: Robert Marko <robimarko@gmail.com>