serial: imx: fix data breakage on termios change

imx_set_termios(): avoid writing baud rate divider registers when the
values to be written are the same as current. Any writing seems to
restart transmission/receiving logic in the hardware, that leads to
data breakage even when rate doesn't in fact change. E.g., user
switches RTS/CTS handshake and suddenly gets broken bytes.

Signed-off-by: Sergey Organov <sorganov@gmail.com>
Link: https://lore.kernel.org/r/1567017475-11919-5-git-send-email-sorganov@gmail.com


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