msm: pcie-ep: Update PCIe pipe clock mux init

PCIe pipe clock mux is dependent on the reference
clocks being on. The pipe clock mux initialization
code was being called before the reference clocks
were initialized. Move the pipe clock mux init until
after the reference clocks have safely switched on.

Change-Id: I6403aa1f208c518793caefb3e3c550cd50577ee0
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>