iommu/vt-d: Fix compile warning from intel-svm.h

The intel_svm_is_pasid_valid() needs to be marked inline, otherwise it
causes the compile warning below:

  CC [M]  drivers/dma/idxd/cdev.o
In file included from drivers/dma/idxd/cdev.c:9:0:
./include/linux/intel-svm.h:125:12: warning: ‘intel_svm_is_pasid_valid’ defined but not used [-Wunused-function]
 static int intel_svm_is_pasid_valid(struct device *dev, int pasid)
            ^~~~~~~~~~~~~~~~~~~~~~~~

Reported-by: Borislav Petkov <bp@alien8.de>
Fixes: 15060aba ('iommu/vt-d: Helper function to query if a pasid has any active users')
Signed-off-by: Joerg Roedel <jroedel@suse.de>