serial: stm32: use port lock wrappers for break control

Commit 30e94586 ("serial: stm32: add support for break control")
added another usage of the port lock, but was merged on the same day as
c5d06662 ("serial: stm32: Use port lock wrappers"), therefore the
latter did not update this usage to use the port lock wrappers.

Fixes: c5d06662 ("serial: stm32: Use port lock wrappers")
Cc: stable <stable@kernel.org>
Signed-off-by: Ben Wolsieffer <ben.wolsieffer@hefring.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Link: https://lore.kernel.org/r/20241216145323.111612-1-ben.wolsieffer@hefring.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>