ASoC: msm: Loopback Driver Reg Stream in Prepare Stage

Move the msm_pcm_routing_reg_phy_stream() to prepare stage.
Then it allows to set channel mixer configuration pre usecase start.

Change-Id: I1811c4d9bcbdd2bb1ee425044407a2c61e794a9a
Signed-off-by: Cong Tang <congt@codeaurora.org>
Signed-off-by: Viraja Kommaraju <virajak@codeaurora.org>