Fix printing the MSI capability.

Fix printing the MSI capability.

Contributed by Matthew Wilcox. His changelog says:

I'd like to present this change for your consideration.  I'm not sure
where the original idea comes from that MSI has a 'queue' of interrupts.
It has multiple independent interrupts.  Also, rather than just dumping
the raw values from the register, it makes sense to decode them into
the number of interrupts it supports.