genirq: Add lost hunk to irq_forced_thread_fn().

The irq_settings_no_softirq_call() related handling got lost in process,
here are the missing bits.

Reported-by: Martin Kaistra <martin.kaistra@linutronix.de>
Fixes: b0cf5c230e2a0 ("Merge tag 'v4.19.183' into linux-4.19.y-rt")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Clark Williams <williams@redhat.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>