regulator: act8945a-regulator: fix 'defined but not used' compiler warning

Fix 'defined but not used' compiler warning for act8945a_suspend()
function in case CONFIG_PM_SLEEP is not defined.

Fixes: b5ebba46 ("regulator: act8945a-regulator: add shutdown function")
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Reported-by: Andrei Stefanescu <andrei.stefanescu@microchip.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/act8945a-regulator.c

@@ -326,7 +326,7 @@ static int act8945a_pmic_probe(struct platform_device *pdev)
 	return regmap_write(act8945a->regmap, ACT8945A_SYS_UNLK_REGS, 0xef);
 }
 
-static int act8945a_suspend(struct device *pdev)
+static int __maybe_unused act8945a_suspend(struct device *pdev)
 {
 	struct act8945a_pmic *act8945a = dev_get_drvdata(pdev);