platform/x86: i2c-multi-instantiate: Accept errors of i2c_acpi_new_device()

In the future i2c_acpi_new_device() will return error pointer in some cases.
Prepare i2c-multi-instantiate driver to support that.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>