Revert "8250: Fix tcsetattr to avoid ioctl(TIOCMIWAIT) hang"

This reverts commit 47d3904f.

Crashes any x86 serial console bootup:

  Console: colour VGA+ 80x25
  BUG: unable to handle kernel NULL pointer dereference at 0000000000000158
  IP: [<ffffffff811ebcb4>] serial8250_do_set_termios+0x1d4/0x430
  ...
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Greg KH <gregkh@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/serial/8250.c

@@ -2343,11 +2343,8 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
 
 	/*
 	 * CTS flow control flag and modem status interrupts
-	 * Only disable MSI if no threads are waiting in
-	 * serial_core::uart_wait_modem_status
 	 */
-	if (!waitqueue_active(&up->port.state->port.delta_msr_wait))
-		up->ier &= ~UART_IER_MSI;
+	up->ier &= ~UART_IER_MSI;
 	if (!(up->bugs & UART_BUG_NOMSR) &&
 			UART_ENABLE_MS(&up->port, termios->c_cflag))
 		up->ier |= UART_IER_MSI;