ASoC: wcd-mbhc: correct detection logic for headphone

Report cable as headphone only if there is button 0
press interrupt. Otherwise SW cannot differentiate between
normal GND-MIC swap and 3 pole extension cable.

CRs-Fixed: 1063474
Change-Id: I63450a94ccbf6c25b935d06dc16b3a26b1d076e3
Signed-off-by: Yeleswarapu Nagaradhesh <nagaradh@codeaurora.org>