iommu/riscv: Fixup compile warning

When __BITS_PER_LONG == 32, size_t is defined as unsigned int rather
than unsigned long. Therefore, we should use size_t to avoid
type-checking errors.

Fixes: 488ffbf ("iommu/riscv: Paging domain support")
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Cc: Tomasz Jeznach <tjeznach@rivosinc.com>
Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
Reviewed-by: Tomasz Jeznach <tjeznach@rivosinc.com>
Link: https://lore.kernel.org/r/20250103024616.3359159-1-guoren@kernel.org
Signed-off-by: Joerg Roedel <jroedel@suse.de>

Author: guoren83

drivers/iommu/riscv/iommu.c

@@ -1278,7 +1278,7 @@ static phys_addr_t riscv_iommu_iova_to_phys(struct iommu_domain *iommu_domain,
 					    dma_addr_t iova)
 {
 	struct riscv_iommu_domain *domain = iommu_domain_to_riscv(iommu_domain);
-	unsigned long pte_size;
+	size_t pte_size;
 	unsigned long *ptr;
 
 	ptr = riscv_iommu_pte_fetch(domain, iova, &pte_size);