ASoC: bolero: Fix higher btn press noise issue

There is higher noise during headset btn press on some
headsets. Change hold time after button release to 600ms
to resolve the noise.

Change-Id: I87e5e13ce39849090da3d3e50ec53e7fd5fdc0e7
Signed-off-by: Vatsal Bucha <vbucha@codeaurora.org>