um: Fix IRQ controller regression on console read

The conversion of UML to use epoll based IRQ controller claimed that
clone_one_chan() can safely call um_free_irq() while starting to ignore
the delay_free_irq parameter that explicitly noted that the IRQ cannot
be freed because this is being called from chan_interrupt(). This
resulted in free_irq() getting called in interrupt context ("Trying to
free IRQ 6 from IRQ context!").

Fix this by restoring previously used delay_free_irq processing.

Fixes: ff6a1798

 ("Epoll based IRQ controller")
Signed-off-by: Jouni Malinen <j@w1.fi>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Richard Weinberger <richard@nod.at>