serial: serial_stm32: Rename status register flags

Uart status register is named USART_ISR on STM32F7, STM32H7
and STM32MP1 SoCs family, but USART_SR only on STM32F4 SoCs.

Use USART_ISR_ prefix instead of USART_SR_ .

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
2 files changed