mfd: intel_soc_pmic: Add CONFIG_PM_SLEEP check for suspend_fn/resume_fn

This patch fix warning message with CONFIG_PM_SLEEP disabled
If CONFIG_PM_SLEEP is not enabled we receive the following warning message:

drivers/mfd/intel_soc_pmic_core.c:118:12:
warning: 'intel_soc_pmic_suspend' defined but not used

Signed-off-by: Jaewon Kim <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

drivers/mfd/intel_soc_pmic_core.c

···
 	return;
 }
 
+#if defined(CONFIG_PM_SLEEP)
 static int intel_soc_pmic_suspend(struct device *dev)
 {
 	struct intel_soc_pmic *pmic = dev_get_drvdata(dev);
···
 
 	return 0;
 }
+#endif
 
 static SIMPLE_DEV_PM_OPS(intel_soc_pmic_pm_ops, intel_soc_pmic_suspend,
 			 intel_soc_pmic_resume);