tty: remove IBSHIFT ifdefs

IBSHIFT is defined by all architectures since commit d0ffb805
("arch/alpha, termios: implement BOTHER, IBSHIFT and termios2").

Reviewed-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20220513082906.11096-4-ilpo.jarvinen@linux.intel.com


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