extcon: Fix hang and extcon_get/set_cable_state().

Users of find_cable_index_by_name() will cause a kernel hang
as the while loop counter is never incremented and end condition
is never reached.

extcon_get_cable_state() and extcon_set_cable_state() are broken
because they use cable index instead of cable id. This causes
the first cable state (cable.0) to be always invalid in sysfs
or extcon_get_cable_state() users.

Introduce a new function find_cable_id_by_name() that fixes
both of the above issues.

Fixes: commit 73b6ecdb ("extcon: Redefine the unique id of supported external connectors without 'enum extcon' type")
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Tested-by: Ivan T. Ivanov <ivan.ivanov@linaro.org>
[cw00.choi: Fix minor coding style]
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>