Unsigned is never less than zero so this error handling won't work.

Fixes: be052cc8 ('extcon: Fix hang and extcon_get/set_cable_state().')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Roger Quadros <rogerq@ti.com>
[cw00.choi: Change the patch title and fix signedness bug of find_cable_index_by_id() ]
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>