iommu/vt-d: Fix compile warning

Make intel_svm_unbind_mm() a static function.

Fixes: 064a57d7 ("iommu/vt-d: Replace intel SVM APIs with generic SVA APIs")
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Acked-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/1590689031-79318-1-git-send-email-jacob.jun.pan@linux.intel.comSigned-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/intel-svm.c

@@ -601,7 +601,7 @@ intel_svm_bind_mm(struct device *dev, int flags, struct svm_dev_ops *ops,
 }
 
 /* Caller must hold pasid_mutex */
-int intel_svm_unbind_mm(struct device *dev, int pasid)
+static int intel_svm_unbind_mm(struct device *dev, int pasid)
 {
 	struct intel_svm_dev *sdev;
 	struct intel_iommu *iommu;