iommu: change iommu_map_sgtable to return signed values

The iommu_map_sgtable() function returns ssize_t and negative error
codes but it's declared as size_t instead.  I think that static checkers
would have complained if this caused a bug, but even though it doesn't
cause a bug, it's definitely worth fixing.
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/06672b96-23fd-424c-8880-1626e7bf119c@moroto.mountainSigned-off-by: Joerg Roedel <jroedel@suse.de>

include/linux/iommu.h

@@ -1116,7 +1116,7 @@ static inline void iommu_free_global_pasid(ioasid_t pasid) {}
  * Creates a mapping at @iova for the buffer described by a scatterlist
  * stored in the given sg_table object in the provided IOMMU domain.
  */
-static inline size_t iommu_map_sgtable(struct iommu_domain *domain,
+static inline ssize_t iommu_map_sgtable(struct iommu_domain *domain,
 			unsigned long iova, struct sg_table *sgt, int prot)
 {
 	return iommu_map_sg(domain, iova, sgt->sgl, sgt->orig_nents, prot,