sfc: Remove write permission from phy_type attribute

Driver probe currently results in:

WARNING: at drivers/base/core.c:576 device_create_file+0x57/0x7e()
Attribute phy_type: write permission without 'store'
Signed-off-by: NBen Hutchings <bhutchings@solarflare.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/sfc/efx.c

@@ -2139,7 +2139,7 @@ show_phy_type(struct device *dev, struct device_attribute *attr, char *buf)
 	struct efx_nic *efx = pci_get_drvdata(to_pci_dev(dev));
 	return sprintf(buf, "%d\n", efx->phy_type);
 }
-static DEVICE_ATTR(phy_type, 0644, show_phy_type, NULL);
+static DEVICE_ATTR(phy_type, 0444, show_phy_type, NULL);
 
 static int efx_register_netdev(struct efx_nic *efx)
 {