s5j/serial: fix RX availability check
s5j/serial: fix RX availability check

UFSTAT[7:0] holds the number of data in Rx FIFO, but zero when Rx FIFO
is full. Thus, we need additional check on UFSTAT[8] bit to ensure that
the FIFO is empty, if the count is zero. Otherwise, up_rxavailable() may
return 'false' even when Rx FIFO is full, though it is less likely to
happen.

Change-Id: Iffd65bf356dd840e864553daf8aa9a7f04a0368e
Signed-off-by: Heesub Shin <45471ea77bd08f3d26635f3f5adb40ba41250a2b@samsung.com>

sunghan-chang/TizenRT,davidfather/TizenRT,JeonginKim/TizenRT,JeonginKim/TizenRT,JeongJunSik/TizenRT,yashwanth686007/TizenRTOS,Parkjihooni6186/TizenRT,jeongarmy/TizenRT,Parkjihooni6186/TizenRT,jsdosa/TizenRT,jsdosa/TizenRT,davidfather/TizenRT,jsdosa/TizenRT,Parkjihooni6186/TizenRT,Samsung/TizenRT,HONGCHAEHEE/TizenRT,chanijjani/TizenRT,yashwanth686007/TizenRTOS,Samsung/TizenRT,JeongJunSik/TizenRT,chanijjani/TizenRT,JeonginKim/TizenRT,shivgarg/TizenRT,jeongarmy/TizenRT,junmin-kim/TizenRT,Samsung/TizenRT,shivgarg/TizenRT,Parkjihooni6186/TizenRT,btheosam/TizenRT,an4967/TizenRT,pillip8282/TizenRT,junmin-kim/TizenRT,jsdosa/TizenRT,btheosam/TizenRT,sunghan-chang/TizenRT,HONGCHAEHEE/TizenRT,pillip8282/TizenRT,JeonginKim/TizenRT,heejin-kim/TizenRT,yashwanth686007/TizenRTOS,Samsung/TizenRT,jeongchanKim/TizenRT,chanijjani/TizenRT,heejin-kim/TizenRT,jeongarmy/TizenRT,btheosam/TizenRT,jsdosa/TizenRT,JeongJunSik/TizenRT,an4967/TizenRT,Samsung/TizenRT,HONGCHAEHEE/TizenRT,junmin-kim/TizenRT,jeongchanKim/TizenRT,jeongarmy/TizenRT,junmin-kim/TizenRT,davidfather/TizenRT,heejin-kim/TizenRT,heejin-kim/TizenRT,chanijjani/TizenRT,heejin-kim/TizenRT,yashwanth686007/TizenRTOS,yashwanth686007/TizenRTOS,Samsung/TizenRT,davidfather/TizenRT,jeongchanKim/TizenRT,JeonginKim/TizenRT,pillip8282/TizenRT,lokeshbv/TizenRT,junmin-kim/TizenRT,shivgarg/TizenRT,HONGCHAEHEE/TizenRT,jeongchanKim/TizenRT,HONGCHAEHEE/TizenRT,chanijjani/TizenRT,jeongarmy/TizenRT,btheosam/TizenRT,shivgarg/TizenRT,davidfather/TizenRT,chanijjani/TizenRT,Parkjihooni6186/TizenRT,an4967/TizenRT,lokeshbv/TizenRT,lokeshbv/TizenRT,davidfather/TizenRT,jsdosa/TizenRT,an4967/TizenRT,lokeshbv/TizenRT,pillip8282/TizenRT,Samsung/TizenRT,jeongchanKim/TizenRT,an4967/TizenRT,lokeshbv/TizenRT,shivgarg/TizenRT,JeonginKim/TizenRT,pillip8282/TizenRT,junmin-kim/TizenRT,jeongarmy/TizenRT,davidfather/TizenRT,sunghan-chang/TizenRT,yashwanth686007/TizenRTOS,btheosam/TizenRT,HONGCHAEHEE/TizenRT,JeongJunSik/TizenRT,jsdosa/TizenRT,sunghan-chang/TizenRT,sunghan-chang/TizenRT,sunghan-chang/TizenRT,jeongarmy/TizenRT,Parkjihooni6186/TizenRT,lokeshbv/TizenRT,heejin-kim/TizenRT,btheosam/TizenRT,sunghan-chang/TizenRT,chanijjani/TizenRT,junmin-kim/TizenRT,an4967/TizenRT,jeongchanKim/TizenRT,shivgarg/TizenRT,pillip8282/TizenRT,jeongchanKim/TizenRT,JeongJunSik/TizenRT,pillip8282/TizenRT,JeongJunSik/TizenRT,an4967/TizenRT