genirq: Fix can_request_irq() for IRQs without an action

commit 2779db8d37d4b542d9ca2575f5f178dbeaca6c86 upstream.

Commit 02725e7471b8 ('genirq: Use irq_get/put functions'),
inadvertently changed can_request_irq() to return 0 for IRQs that have
no action.  This causes pcibios_lookup_irq() to select only IRQs that
already have an action with IRQF_SHARED set, or to fail if there are
none.  Change can_request_irq() to return 1 for IRQs that have no
action (if the first two conditions are met).

Reported-by: Bjarni Ingi Gislason <bjarniig@rhi.hi.is>
Tested-by: Bjarni Ingi Gislason <bjarniig@rhi.hi.is> (against 3.2)
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: 709647@bugs.debian.org
Link: http://bugs.debian.org/709647
Link: http://lkml.kernel.org/r/1372383630.23847.40.camel@deadeye.wl.decadent.org.uk
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>