If you have a controller with one channel disabled and unmapped the new
iomap code blindly tries to iomap unconfigured BARs. Later on the code
does the right thing and checks for unmapped bars but it is done in the
wrong order

Reorder the checks and make the iomap conditional

Tejun: I think the code below is now correct but would appreciate you
giving it a review.
Signed-off-by: Alan Cox <alan@redhat.com>
Acked-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>