platform/chrome: cros_ec: remove unneeded label and if-condition

Both `ec_dev->ec` and `ec_dev->pd` are initialized to NULL at the
beginning of cros_ec_register().  Also, platform_device_unregister()
takes care if the given platform_device is NULL.

Remove the unneeded goto-label and if-condition.

Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Link: https://lore.kernel.org/r/20230308031247.2866401-1-tzungbi@kernel.org