mxs-auart broken in v6.2 and onwards

[Emil Kronborg]

Hi,

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. I
bisected the bad commit to be 2d141e683e9a ("tty: serial: use
uart_port_tx() helper"). Since it concerns multiple drivers, simply
reverting it is not feasible. One solution would be to effectively
revert the commit for just mxs-auart.c, but maybe you have a better
idea? Any pointers is appreciated.

Regards,
Emil