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: NLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: NJingoo Han <jg1.han@samsung.com>
Signed-off-by: NLee Jones <lee.jones@linaro.org>

drivers/mfd/ab8500-gpadc.c

@@ -888,6 +888,7 @@ static int ab8500_gpadc_runtime_resume(struct device *dev)
 }
 #endif
 
+#ifdef CONFIG_PM_SLEEP
 static int ab8500_gpadc_suspend(struct device *dev)
 {
 	struct ab8500_gpadc *gpadc = dev_get_drvdata(dev);
@@ -915,6 +916,7 @@ static int ab8500_gpadc_resume(struct device *dev)
 	mutex_unlock(&gpadc->ab8500_gpadc_lock);
 	return ret;
 }
+#endif
 
 static int ab8500_gpadc_probe(struct platform_device *pdev)
 {