serial: mxs-auart: fix tx

serial: mxs-auart: fix tx

Emil reports:
  After updating Linux on an i.MX28 board, serial communication over
  AUART broke. When I TX from the board and measure on the TX pin, it
  seems like the HW fifo is not emptied before the transmission is
  stopped.

MXS performs weird things with stop_tx(). The driver makes it
conditional on uart_tx_stopped().

So the driver needs special handling. Pass the brand new UART_TX_NOSTOP
to uart_port_tx_flags() and handle the stop on its own.

Signed-off-by: "Jiri Slaby (SUSE)" <[email protected]>
Reported-by: Emil Kronborg <[email protected]>
Cc: stable <[email protected]>
Fixes: 2d141e683e9a ("tty: serial: use uart_port_tx() helper")
Closes: https://lore.kernel.org/all/miwgbnvy3hjpnricubg76ytpn7xoceehwahupy25bubbduu23s@om2lptpa26xw/
Tested-by: Stefan Wahren <[email protected]>
Tested-by: Emil Kronborg <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>