openpic: always call IRQ_check from IRQ_get_next

Previously the code relied on the queue's "next" field getting
set to -1 sometime between an update to the bitmap, and the next
call to IRQ_get_next.  Sometimes this happened after the update.
Sometimes it happened before the check.  Sometimes it didn't happen
at all.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
