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
134fac3f457f3dd753ecdb25e6da3e5f6629f696 (PCI / Intel IOMMU: Use
syscore_ops instead of sysdev class and sysdev) is not defined
appropriately.  Fix this issue.

Reported-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c
index 59f17ac..f02c34d 100644
--- a/drivers/pci/intel-iommu.c
+++ b/drivers/pci/intel-iommu.c
@@ -3388,7 +3388,7 @@
 }
 
 #else
-static inline int init_iommu_pm_ops(void) { }
+static inline void init_iommu_pm_ops(void) {}
 #endif	/* CONFIG_PM */
 
 /*