serial: sh-sci: Fix unlocked access to SCSCR register
The SCSCR register access in sci_break_ctl() is not locked.
sci_start_tx() and sci_set_termios() changes the SCSCR register,
but does not lock sci_port.
Therefore, this patch adds lock during register access.
Also, remove the log output that leads to a double lock.
Some analysis of where locks are not taken is as follows.
It appears that the lock is not taken in:
- sci_start_tx(), sci_stop_tx() as this is installed as a callback.
And all callers of the callback take the lock.
- start_rx as callers take the lock.
- stop_rx. this is both installed as a callback and called directly.
In both cases the caller takes the lock.