sfc: Const-qualify static data as appropriate, partly prompted by checkpatch

Fix the following warnings:

WARNING: struct dev_pm_ops should normally be const
WARNING: static const char * array should probably be static const char * const

Similarly const-qualify struct i2c_board_info, struct i2c_algo_bit_data,
struct efx_ethtool_stat, struct efx_mtd_ops and struct siena_nvram_type_info.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
diff --git a/drivers/net/ethernet/sfc/ethtool.c b/drivers/net/ethernet/sfc/ethtool.c
index c090de4..52c9ee4 100644
--- a/drivers/net/ethernet/sfc/ethtool.c
+++ b/drivers/net/ethernet/sfc/ethtool.c
@@ -91,7 +91,7 @@
 	EFX_ETHTOOL_STAT(tx_##field, tx_queue, field,		\
 			 unsigned int, efx_get_uint_stat)
 
-static struct efx_ethtool_stat efx_ethtool_stats[] = {
+static const struct efx_ethtool_stat efx_ethtool_stats[] = {
 	EFX_ETHTOOL_U64_MAC_STAT(tx_bytes),
 	EFX_ETHTOOL_U64_MAC_STAT(tx_good_bytes),
 	EFX_ETHTOOL_U64_MAC_STAT(tx_bad_bytes),
@@ -486,7 +486,7 @@
 {
 	struct efx_nic *efx = netdev_priv(net_dev);
 	struct efx_mac_stats *mac_stats = &efx->mac_stats;
-	struct efx_ethtool_stat *stat;
+	const struct efx_ethtool_stat *stat;
 	struct efx_channel *channel;
 	struct efx_tx_queue *tx_queue;
 	struct rtnl_link_stats64 temp;