mxser: remove wait for sent from mxser_close_port

mxser: remove wait for sent from mxser_close_port

mxser_close() behaves like this:
  -> tty_port_close_start()
    -> tty_wait_until_sent()
      -> mxser_wait_until_sent()
  -> mxser_close_port
    -> wait for TEMT

So it is already waited for TEMT through mxser_wait_until_sent() and
there is another round of waiting in mxser_close_port(). The latter one
is superfluous as nothing could be filled into the output FIFO. Remove
the call.

This helps unification among drivers (so that all behave the same) and
future use of tty_port_close().

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20211118073125.12283-2-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>