[PATCH v2] mfd: axp20x-i2c: Tell the compiler that ACPI functions may not be used

[Lee Jones]

... as is the case when !CONFIG_ACPI.
    
This squashes the current W=1 kernel builds warning:
    
 drivers/mfd/axp20x-i2c.c:82:36: warning: ‘axp20x_i2c_acpi_match’ defined but 
not used [-Wunused-const-variable=]
    
Cc: Chen-Yu Tsai <w...@csie.org>
Cc: Carlo Caione <ca...@caione.org>
Signed-off-by: Lee Jones <lee.jo...@linaro.org>

diff --git a/drivers/mfd/axp20x-i2c.c b/drivers/mfd/axp20x-i2c.c
index 14f9df74f855c..7d08c06de7afc 100644
--- a/drivers/mfd/axp20x-i2c.c
+++ b/drivers/mfd/axp20x-i2c.c
@@ -79,7 +79,7 @@ static const struct i2c_device_id axp20x_i2c_id[] = {
 };
 MODULE_DEVICE_TABLE(i2c, axp20x_i2c_id);
 
-static const struct acpi_device_id axp20x_i2c_acpi_match[] = {
+static const struct acpi_device_id __maybe_unused axp20x_i2c_acpi_match[] = {
        {
                .id = "INT33F4",
                .driver_data = AXP288_ID,