iommu/omap: Fix compilation warnings

A recent patch introduced a new compiler warning because
two functions with non-void return type have no return
statement in omap-iommu.h for CONFIG_OMAP_IOMMU=n.

Fix this by adding return statements to these functions.

Fixes: d9c4d8a6cc ('iommu/omap: introduce new API for runtime suspend/resume control')
Signed-off-by: Joerg Roedel <jroedel@suse.de>

include/linux/omap-iommu.h

@@ -22,8 +22,15 @@ int omap_iommu_domain_activate(struct iommu_domain *domain);
 static inline void omap_iommu_save_ctx(struct device *dev) {}
 static inline void omap_iommu_restore_ctx(struct device *dev) {}
 
-static inline int omap_iommu_domain_deactivate(struct iommu_domain *domain) {}
-static inline int omap_iommu_domain_activate(struct iommu_domain *domain) {}
+static inline int omap_iommu_domain_deactivate(struct iommu_domain *domain)
+{
+	return -ENODEV;
+}
+
+static inline int omap_iommu_domain_activate(struct iommu_domain *domain)
+{
+	return -ENODEV;
+}
 #endif
 
 #endif