ASoC: msm8x16-wcd: fix headset playback issue on cajon 2.0

On pmic/cajon 2.0, headset record is failing due to mux setting is
not taking effect. As HPH MUX is not mapped to any register from
codec hardware, it needs to be declared as SND_SOC_NOPM mux.

Change-Id: Ice8e749d9861bf6eeb020818ad30f55e7f62e25b
Signed-off-by: Simmi Pateriya <simmip@codeaurora.org>