iommu: Modify the description of iommu_sva_unbind_device

iommu_sva_unbind_device has no return value.

Remove the description of the return value of the function.
Signed-off-by: NChen Jun <c00424029@huawei.com>
Link: https://lore.kernel.org/r/20201023064827.74794-1-chenjun102@huawei.comSigned-off-by: NWill Deacon <will@kernel.org>

drivers/iommu/iommu.c

@@ -2995,8 +2995,6 @@ EXPORT_SYMBOL_GPL(iommu_sva_bind_device);
  * Put reference to a bond between device and address space. The device should
  * not be issuing any more transaction for this PASID. All outstanding page
  * requests for this PASID must have been flushed to the IOMMU.
- *
- * Returns 0 on success, or an error value
  */
 void iommu_sva_unbind_device(struct iommu_sva *handle)
 {