mlxsw: core: Change BUG to WARN in hwmon code

Better to just warn the user that something really odd is going on and
continue to run.

Suggested-by: Or Gerlitz <[e-mail]>
Signed-off-by: Jiri Pirko <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ethernet/mellanox/mlxsw/core_hwmon.c

···
 			 "pwm%u", num + 1);
 		break;
 	default:
-		BUG();
+		WARN_ON(1);
 	}
 
 	mlxsw_hwmon_attr->type_index = type_index;