soundwire: intel: fix intel_suspend/resume defined but not used warning

When CONFIG_PM_SLEEP is not defined, GCC throws compilation warnings:

drivers/soundwire/intel.c:1799:12: warning: ‘intel_resume’ defined but not
used [-Wunused-function]
 static int intel_resume(struct device *dev)
            ^~~~~~~~~~~~
drivers/soundwire/intel.c:1683:12: warning: ‘intel_suspend’ defined but not
used [-Wunused-function]
 static int intel_suspend(struct device *dev)
            ^~~~~~~~~~~~~

Fix by using __maybe_unused macro.
Suggested-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200824133234.28115-1-yung-chuan.liao@linux.intel.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/soundwire/intel.c

@@ -1527,7 +1527,7 @@ int intel_master_process_wakeen_event(struct platform_device *pdev)
 
 #ifdef CONFIG_PM
 
-static int intel_suspend(struct device *dev)
+static int __maybe_unused intel_suspend(struct device *dev)
 {
 	struct sdw_cdns *cdns = dev_get_drvdata(dev);
 	struct sdw_intel *sdw = cdns_to_intel(cdns);
@@ -1625,7 +1625,7 @@ static int intel_suspend_runtime(struct device *dev)
 	return ret;
 }
 
-static int intel_resume(struct device *dev)
+static int __maybe_unused intel_resume(struct device *dev)
 {
 	struct sdw_cdns *cdns = dev_get_drvdata(dev);
 	struct sdw_intel *sdw = cdns_to_intel(cdns);