ASoC: wcd: donot disable PDM clk on power down

During MT call if pdm clock is disabled by power down sequence
of RX path,RX on headphones will not work.So donot disable the clock
during power down sequence of RX path.

CRs-Fixed: 641527
Change-Id: Id138d8179a895bbf2a5f4d445febf92ab42884e2
Signed-off-by: Yeleswarapu Nagaradhesh <nagaradh@codeaurora.org>