serial: stm32: clean wakeup handling in serial_suspend

serial: stm32: clean wakeup handling in serial_suspend

Remove useless call to stm32_usart_serial_en_wakeup() routine in suspend
callback. When called with "false" argument, this routine is clearing UESM
and WUFIE bits if usart is not wakeup source. Those bits are already
cleared in set_termios(), and then in serial_resume() callback when usart
is wakeup source.

Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>
Signed-off-by: Erwan Le Ray <erwan.leray@foss.st.com>
Link: https://lore.kernel.org/r/20210319184253.5841-3-erwan.leray@foss.st.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>