serial: 8250_tegra: mark acpi_device_id as unused with !ACPI

The driver's acpi_device_id table is referenced via ACPI_PTR() so it
will be unused for !CONFIG_ACPI builds:

  drivers/tty/serial/8250/8250_tegra.c:178:36:
    warning: ‘tegra_uart_acpi_match’ defined but not used [-Wunused-const-variable=]
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20220308074157.113568-1-krzysztof.kozlowski@canonical.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_tegra.c

@@ -175,7 +175,7 @@ static const struct of_device_id tegra_uart_of_match[] = {
 };
 MODULE_DEVICE_TABLE(of, tegra_uart_of_match);
 
-static const struct acpi_device_id tegra_uart_acpi_match[] = {
+static const struct acpi_device_id tegra_uart_acpi_match[] __maybe_unused = {
 	{ "NVDA0100", 0 },
 	{ },
 };