TTY: simserial, remove IRQ_T

We do not set ASYNC_SHARE_IRQ anywhere. And since IRQF_DISABLED is a
noop, pass zero to request_irq directly instead of this ugly macro.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>