mxser: drop UART_MCR_AFE and UART_LSR_SPECIAL defines

* UART_MCR_AFE is a redefinition of serial_reg.h's one.
* UART_LSR_SPECIAL is a redefinition of serial_reg.h's
  UART_LSR_BRK_ERROR_BITS.

So remove both and replace the latter uses by already defined
UART_LSR_BRK_ERROR_BITS.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20210618061516.662-21-jslaby@suse.cz


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