Currently assign_irq_vector works mostly by side effect and returns
the results of it's changes to the caller.  Which makes for a lot of
arguments to pass/return and confusion as to what to do if you need
the status but you aren't calling assign_irq_vector.

This patch stops returning values from assign_irq_vector that can be
retrieved just as easily by examining irq_cfg, and modifies the
callers to retrive those values from irq_cfg when they need them.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>