platform/chrome: cros_ec_dev - utilize new cdev_device_add helper function
Replace the open coded registration of the cdev and dev with the
new device_add_cdev() helper. The helper replaces a common pattern by
taking the proper reference against the parent device and adding both
the cdev and the device.
At the same time we cleanup the error path through device_probe
function: we use put_device instead of kfree directly as recommended
by the device_initialize documentation.