iommu/riscv: prevent NULL deref in iova_to_phys

The riscv_iommu_pte_fetch() function returns either NULL for
unmapped/never-mapped iova, or a valid leaf pte pointer that
requires no further validation.

riscv_iommu_iova_to_phys() failed to handle NULL returns.
Prevent null pointer dereference in
riscv_iommu_iova_to_phys(), and remove the pte validation.

Fixes: 488ffbf ("iommu/riscv: Paging domain support")
Cc: Tomasz Jeznach <tjeznach@rivosinc.com>
Signed-off-by: XianLiang Huang <huangxianliang@lanxincomputing.com>
Link: https://lore.kernel.org/r/20250820072248.312-1-huangxianliang@lanxincomputing.com
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

Author: XianLiang Huang

drivers/iommu/riscv/iommu.c

@@ -1283,7 +1283,7 @@ static phys_addr_t riscv_iommu_iova_to_phys(struct iommu_domain *iommu_domain,
 	unsigned long *ptr;
 
 	ptr = riscv_iommu_pte_fetch(domain, iova, &pte_size);
-	if (_io_pte_none(*ptr) || !_io_pte_present(*ptr))
+	if (!ptr)
 		return 0;
 
 	return pfn_to_phys(__page_val_to_pfn(*ptr)) | (iova & (pte_size - 1));