ASoC: mdm9615: Fix GPIO headset detection

GPIO headset detection is not enabled because headset
initialization code is executed before GPIO HS
detection mode is set in machine driver. Set GPIO
headset detection mode before headset initialization.

CRs-fixed: 479625
Change-Id: I499dc9b8e65e6929f244eb0633269bcce7430b5e
Signed-off-by: Prashanth Reddy <pgreddy@codeaurora.org>