PM / Intel IOMMU: Fix init_iommu_pm_ops() for CONFIG_PM unset

If CONFIG_PM is not set, init_iommu_pm_ops() introduced by commit
134fac3f (PCI / Intel IOMMU: Use
syscore_ops instead of sysdev class and sysdev) is not defined
appropriately.  Fix this issue.
Reported-by: NTony Luck <tony.luck@intel.com>
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>

drivers/pci/intel-iommu.c

@@ -3388,7 +3388,7 @@ static void __init init_iommu_pm_ops(void)
 }
 
 #else
-static inline int init_iommu_pm_ops(void) { }
+static inline void init_iommu_pm_ops(void) {}
 #endif	/* CONFIG_PM */
 
 /*