sfc: Support variable-length response to MCDI GET_BOARD_CFG

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
diff --git a/drivers/net/ethernet/sfc/mtd.c b/drivers/net/ethernet/sfc/mtd.c
index 7581483..8f4604d 100644
--- a/drivers/net/ethernet/sfc/mtd.c
+++ b/drivers/net/ethernet/sfc/mtd.c
@@ -627,7 +627,8 @@
 				     struct efx_mtd *efx_mtd)
 {
 	struct efx_mtd_partition *part;
-	uint16_t fw_subtype_list[MC_CMD_GET_BOARD_CFG_OUT_FW_SUBTYPE_LIST_MINNUM];
+	uint16_t fw_subtype_list[
+		MC_CMD_GET_BOARD_CFG_OUT_FW_SUBTYPE_LIST_MAXNUM];
 	int rc;
 
 	rc = efx_mcdi_get_board_cfg(efx, NULL, fw_subtype_list, NULL);