drivers: regulator: npm1100: regulator device may be unused

Since nPM1100 may be configured statically in some circuits, BUCK node
may note be defined, so neither API ops or init call are used in the
code. Add __unused attribute to account for such case.

Signed-off-by: Gerard Marull-Paretas <[email protected]>

Author: gmarull

drivers/regulator/regulator_npm1100.c

@@ -10,6 +10,7 @@
 #include <zephyr/drivers/gpio.h>
 #include <zephyr/drivers/regulator.h>
 #include <zephyr/dt-bindings/regulator/npm1100.h>
+#include <zephyr/toolchain.h>
 
 struct regulator_npm1100_pconfig {
 	struct gpio_dt_spec iset;
@@ -57,7 +58,7 @@ static int regulator_npm1100_get_mode(const struct device *dev,
 	return 0;
 }
 
-static int regulator_npm1100_init(const struct device *dev)
+static __unused int regulator_npm1100_init(const struct device *dev)
 {
 	const struct regulator_npm1100_config *config = dev->config;
 	int ret;
@@ -100,7 +101,7 @@ static int regulator_npm1100_common_init(const struct device *dev)
 	return 0;
 }
 
-static const struct regulator_driver_api api = {
+static const __unused struct regulator_driver_api api = {
 	.set_mode = regulator_npm1100_set_mode,
 	.get_mode = regulator_npm1100_get_mode,
 };