[ Upstream commitb83b957c91] Disables the tx irq when the transmission is ended and updates stop_tx conditions for code cleanup. Fixes:48a6092fb4("serial: stm32-usart: Add STM32 USART Driver") Signed-off-by: Erwan Le Ray <erwan.leray@st.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org>