fs/select: fix select build fail if debug mode is disabled
fs/select: fix select build fail if debug mode is disabled

ndx is not used if debug mode is disabled. so add additional check
code in release mode.

junmin-kim/TizenRT,jsdosa/TizenRT,junmin-kim/TizenRT,jeongchanKim/TizenRT,jeongarmy/TizenRT,jeongarmy/TizenRT,an4967/TizenRT,jeongchanKim/TizenRT,jeongchanKim/TizenRT,junmin-kim/TizenRT,Samsung/TizenRT,jsdosa/TizenRT,an4967/TizenRT,jeongchanKim/TizenRT,jeongarmy/TizenRT,junmin-kim/TizenRT,Samsung/TizenRT,jeongarmy/TizenRT,jeongchanKim/TizenRT,an4967/TizenRT,sunghan-chang/TizenRT,junmin-kim/TizenRT,Samsung/TizenRT,Samsung/TizenRT,jsdosa/TizenRT,Samsung/TizenRT,sunghan-chang/TizenRT,pillip8282/TizenRT,Samsung/TizenRT,pillip8282/TizenRT,an4967/TizenRT,jeongarmy/TizenRT,jsdosa/TizenRT,pillip8282/TizenRT,sunghan-chang/TizenRT,pillip8282/TizenRT,jeongarmy/TizenRT,sunghan-chang/TizenRT,an4967/TizenRT,sunghan-chang/TizenRT,sunghan-chang/TizenRT,jsdosa/TizenRT,junmin-kim/TizenRT,jsdosa/TizenRT,pillip8282/TizenRT,sunghan-chang/TizenRT,an4967/TizenRT,jeongarmy/TizenRT,pillip8282/TizenRT,jeongchanKim/TizenRT,Samsung/TizenRT,jsdosa/TizenRT,jeongchanKim/TizenRT,pillip8282/TizenRT,junmin-kim/TizenRT,an4967/TizenRT