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/selftest.c b/drivers/net/ethernet/sfc/selftest.c
index fc62fe2..17ff9b3 100644
--- a/drivers/net/ethernet/sfc/selftest.c
+++ b/drivers/net/ethernet/sfc/selftest.c
@@ -50,7 +50,7 @@
 
 /* Interrupt mode names */
 static const unsigned int efx_interrupt_mode_max = EFX_INT_MODE_MAX;
-static const char *efx_interrupt_mode_names[] = {
+static const char *const efx_interrupt_mode_names[] = {
 	[EFX_INT_MODE_MSIX]   = "MSI-X",
 	[EFX_INT_MODE_MSI]    = "MSI",
 	[EFX_INT_MODE_LEGACY] = "legacy",