iommufd: Fix error pointer checking

Smatch static checker reported below warning:

    drivers/iommu/iommufd/fault.c:131 iommufd_device_get_attach_handle()
    warn: 'handle' is an error pointer or valid

Fix it by checking 'handle' with IS_ERR().

Fixes: b7d8833 ("iommufd: Fault-capable hwpt attach/detach/replace")
Link: https://lore.kernel.org/r/[email protected]
Reported-by: Dan Carpenter <[email protected]>
Closes: https://lore.kernel.org/linux-iommu/[email protected]/
Signed-off-by: Lu Baolu <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>

Author: LuBaolu

drivers/iommu/iommufd/fault.c

@@ -128,7 +128,7 @@ iommufd_device_get_attach_handle(struct iommufd_device *idev)
 	struct iommu_attach_handle *handle;
 
 	handle = iommu_attach_handle_get(idev->igroup->group, IOMMU_NO_PASID, 0);
-	if (!handle)
+	if (IS_ERR(handle))
 		return NULL;
 
 	return to_iommufd_handle(handle);