This patch use devm_extcon_dev_allocate() to simplify the memory control
of extcon device.

Cc: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: patches@opensource.wolfsonmicro.com
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Reviewed-by: Felipe Balbi <balbi@ti.com>