extcon: Fix error handling in extcon_dev_register

[ Upstream commit d3bdd1c3 ]

When devm_kcalloc() fails, we should execute device_unregister()
to unregister edev->dev from system.

Fixes: 046050f6

 ("extcon: Update the prototype of extcon_register_notifier() with enum extcon")
Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>