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/net_driver.h b/drivers/net/ethernet/sfc/net_driver.h
index c49502b..9353ce8 100644
--- a/drivers/net/ethernet/sfc/net_driver.h
+++ b/drivers/net/ethernet/sfc/net_driver.h
@@ -395,12 +395,12 @@
 #define STRING_TABLE_LOOKUP(val, member) \
 	((val) < member ## _max) ? member ## _names[val] : "(invalid)"
 
-extern const char *efx_loopback_mode_names[];
+extern const char *const efx_loopback_mode_names[];
 extern const unsigned int efx_loopback_mode_max;
 #define LOOPBACK_MODE(efx) \
 	STRING_TABLE_LOOKUP((efx)->loopback_mode, efx_loopback_mode)
 
-extern const char *efx_reset_type_names[];
+extern const char *const efx_reset_type_names[];
 extern const unsigned int efx_reset_type_max;
 #define RESET_TYPE(type) \
 	STRING_TABLE_LOOKUP(type, efx_reset_type)