mfd: axp20x: Skip of_device_id table when !CONFIG_OF

The driver can match either via ACPI or OF.  Its of_device_id table is
referenced via of_match_ptr() so it will be unused for !CONFIG_OF
builds:

  drivers/mfd/axp20x-i2c.c:60:34: warning: ‘axp20x_i2c_of_match’ defined but not used [-Wunused-const-variable=]
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/axp20x-i2c.c

@@ -57,6 +57,7 @@ static int axp20x_i2c_remove(struct i2c_client *i2c)
 	return axp20x_device_remove(axp20x);
 }
 
+#ifdef CONFIG_OF
 static const struct of_device_id axp20x_i2c_of_match[] = {
 	{ .compatible = "x-powers,axp152", .data = (void *)AXP152_ID },
 	{ .compatible = "x-powers,axp202", .data = (void *)AXP202_ID },
@@ -68,6 +69,7 @@ static const struct of_device_id axp20x_i2c_of_match[] = {
 	{ },
 };
 MODULE_DEVICE_TABLE(of, axp20x_i2c_of_match);
+#endif
 
 static const struct i2c_device_id axp20x_i2c_id[] = {
 	{ "axp152", 0 },