extcon: max77843: Fix an error code in max77843_init_muic_regmap()

The i2c_new_dummy() return the NULL if error happen. So, If i2c_new_dummy()
return NULL, max77843_init_muic_regmap() return the proper error value
(-ENOMEM);

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
[cw00.choi: Use -ENOMEM instead of -ENODEV and modify patch description]
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>