drivers: nrf: nrf uarte fix TX interrupts disabling.
drivers: nrf: nrf uarte fix TX interrupts disabling.

Make sure that TX interrupts are disabled after transmission
is finished.

Signed-off-by: Mieszko Mierunski <0153720f373f9fb33402fd56a3b748bfb748366c@nordicsemi.no>

ldts/zephyr,explora26/zephyr,punitvara/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,finikorg/zephyr,Vudentz/zephyr,explora26/zephyr,ldts/zephyr,nashif/zephyr,galak/zephyr,Vudentz/zephyr,punitvara/zephyr,finikorg/zephyr,explora26/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,punitvara/zephyr,GiulianoFranchetto/zephyr,GiulianoFranchetto/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,explora26/zephyr,finikorg/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,galak/zephyr,ldts/zephyr,ldts/zephyr,galak/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,punitvara/zephyr,finikorg/zephyr,Vudentz/zephyr,Vudentz/zephyr,galak/zephyr