extcon: max8997: use dev_err() instead of pr_err()

dev_err() is more preferred than pr_err().

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Myungjoo Ham <myungjoo.ham@samsung.com>