ASoC: rt5640: Omit ACPI match table only if !ACPI

The ACPI_PTR() macro evaluates to NULL if ACPI is disabled and hence the
ACPI match table won't be used, causing the compiler to complain. Avoid
this by protecting the table using an #ifdef CONFIG_ACPI.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Mark Brown <broonie@linaro.org>