sfc: Improve test for IOMMU in use

The device::iommu_group field may be set even if no IOMMU is in use.
iommu_present() is still a better indicator, although it doesn't tell
us whether *our* device is affected.

Reported-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

drivers/net/ethernet/sfc/rx.c

@@ -677,7 +677,7 @@ static void efx_init_rx_recycle_ring(struct efx_nic *efx,
 #ifdef CONFIG_PPC64
 	bufs_in_recycle_ring = EFX_RECYCLE_RING_SIZE_IOMMU;
 #else
-	if (efx->pci_dev->dev.iommu_group)
+	if (iommu_present(&pci_bus_type))
 		bufs_in_recycle_ring = EFX_RECYCLE_RING_SIZE_IOMMU;
 	else
 		bufs_in_recycle_ring = EFX_RECYCLE_RING_SIZE_NOIOMMU;