clk: qcom: Add xo dummy clk on msm8998

We have this dummy factor clk in place to workaround a missing rpm clk
driver that can manage the XO clk state. Add it in to match what we do
on msm8996.

Cc: Jeffrey Hugo <jhugo@codeaurora.org>
Cc: Marc Gonzalez <marc.w.gonzalez@free.fr>
Tested-by: Jeffrey Hugo <jhugo@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>