ASoC: wcd937x: Fix pop after PDR

Pop is heard after PDR is triggered. This is
because while device down PA is still on.
Disable PA before SSR Device Down to prevent pop.

Change-Id: I6bfe3e731bdf60fba8fee90ab39c03a0512006ce
Signed-off-by: Vatsal Bucha <vbucha@codeaurora.org>