iommu: Fix IOMMU sysfs stubs

0-day kernel build testing reports:

   arch/x86/kvm/x86.o: In function `iommu_device_destroy':
>> (.text+0x7a0a): multiple definition of `iommu_device_destroy'
   arch/x86/kvm/../../../virt/kvm/vfio.o:vfio.c:(.text+0x490): first defined here
   arch/x86/kvm/x86.o: In function `iommu_device_link':
>> (.text+0x7a15): multiple definition of `iommu_device_link'
   arch/x86/kvm/../../../virt/kvm/vfio.o:vfio.c:(.text+0x49b): first defined here
   arch/x86/kvm/x86.o: In function `iommu_device_unlink':
>> (.text+0x7a25): multiple definition of `iommu_device_unlink'
   arch/x86/kvm/../../../virt/kvm/vfio.o:vfio.c:(.text+0x4ab): first defined here
   arch/x86/kvm/x86.o: In function `iommu_device_create':
>> (.text+0x79f8): multiple definition of `iommu_device_create'
   arch/x86/kvm/../../../virt/kvm/vfio.o:vfio.c:(.text+0x47e): first defined here

These are due to failing to define the stubs as static inline.  Fix.
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

include/linux/iommu.h

@@ -403,23 +403,24 @@ static inline int iommu_domain_set_attr(struct iommu_domain *domain,
 	return -EINVAL;
 }
 
-struct device *iommu_device_create(struct device *parent, void *drvdata,
+static inline struct device *iommu_device_create(struct device *parent,
+					void *drvdata,
 					const struct attribute_group **groups,
 					const char *fmt, ...)
 {
 	return ERR_PTR(-ENODEV);
 }
 
-void iommu_device_destroy(struct device *dev)
+static inline void iommu_device_destroy(struct device *dev)
 {
 }
 
-int iommu_device_link(struct device *dev, struct device *link)
+static inline int iommu_device_link(struct device *dev, struct device *link)
 {
 	return -EINVAL;
 }
 
-void iommu_device_unlink(struct device *dev, struct device *link)
+static inline void iommu_device_unlink(struct device *dev, struct device *link)
 {
 }