serial: stm32: fix rx error handling

- Fixes parity and framing error bit by clearing parity and framing error
  flag. The current implementation doesn't clear the error bits when an
  error is detected.
- Fixes the incorrect name of framing error clearing flag in header file.
- Fixes misalignement between data frame and errors status. The status
  read for "n" frame was the status of "n+1" frame".
- Fixes break detection was not triggered by the expected register.

Fixes: 48a6092f ("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>