Input: pcf8574_keypad - fix error handling in pcf8574_kp_probe

It is not allowed to call input_free_device() after calling
input_unregister_device() because input devices are refcounted and
unregister will free the device if we were holding he last referenc.

The preferred style in input/ is to make input_register_device() the
last function in the probe which can fail.  That way we don't need to
call input_unregister_device().

Also do not need to call input_set_drvdata() as nothing in the driver
uses the data.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>