ASoC: wcd: enable current source for headphone

If headset is detected as headphone during slow insertion,
could not get button release interrupt on complete insertion
of headset.So enable CS to get button release interrupt.

CRs-Fixed: 705961
Change-Id: I951c34723cc0329f69fff33a479d7702928b6f7c
Signed-off-by: Yeleswarapu Nagaradhesh <nagaradh@codeaurora.org>