mfd: ab8500-gpadc: Add CONFIG_PM_SLEEP to suspend/resume

Add CONFIG_PM_SLEEP to suspend/resume functions to fix the build
warnings when CONFIG_PM_SLEEP is not selected. This is because
sleep PM callbacks defined by SET_SYSTEM_SLEEP_PM_OPS are only used
when the CONFIG_PM_SLEEP is enabled.

drivers/mfd/ab8500-gpadc.c:891:12: warning: 'ab8500_gpadc_suspend' defined but not used [-Wunused-function]
drivers/mfd/ab8500-gpadc.c:903:12: warning: 'ab8500_gpadc_resume' defined but not used [-Wunused-function]

Acked-by: Linus Walleij <[e-mail]>
Signed-off-by: Jingoo Han <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

drivers/mfd/ab8500-gpadc.c

···
 }
 #endif
 
+#ifdef CONFIG_PM_SLEEP
 static int ab8500_gpadc_suspend(struct device *dev)
 {
 	struct ab8500_gpadc *gpadc = dev_get_drvdata(dev);
···
 	mutex_unlock(&gpadc->ab8500_gpadc_lock);
 	return ret;
 }
+#endif
 
 static int ab8500_gpadc_probe(struct platform_device *pdev)
 {