AHCI: Make distinct names for ports in /proc/interrupts

Currently all interrupts assigned to AHCI ports show up in
'/proc/interrupts' as 'ahci'. This fix adds port numbers as
suffixes and hence makes the descriptions distinct.

Reported-by: Jan Beulich <JBeulich@suse.com>
Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>