platform/x86: i2c-multi-instantiate: Get rid of obsolete conditional

Now, when i2c_acpi_new_device() never returns NULL, there is no point to check
for it. Besides that, i2c_acpi_new_device() returns -EPROBE_DEFER directly and
caller doesn't need to guess is better.

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>