The kernel oopses if this flag is set.

[and neither driver should set it as they call tty_flip_buffer_push from IRQ
 paths so have always been buggy]
Signed-off-by: Chuck Ebbert <cebbert@redhat.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>