tty: replace in_irq() with in_hardirq()

Replace the obsolete and ambiguos macro in_irq() with new
macro in_hardirq().

Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: Changbin Du <changbin.du@gmail.com>
Link: https://lore.kernel.org/r/20210814005033.2381-1-changbin.du@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>