clk: msm: clock-gcc: Set post divider for debug mux for MSMGold

Debug mux post_div needs to be set to 4 in order to measure
the frequency of a clock that has high clock rate correctly,
so update the post divider for MSMGold.

CRs-Fixed: 977413
Change-Id: I60b89bbd563d88c14dbef7c677578e91769b3e37
Signed-off-by: Odelu Kukatla <okukatla@codeaurora.org>