Change the required minimum number of MSI/MSIX interrupt vectors from
2 to 1; the admin queue and first I/O queue actually share vector 0.
Also change the max_qid assignment, to equal the number of vectors.
Since the number of vectors is set to the number of cpus, on a system
with only 1 cpu the previous code is guaranteed to fail, since there
will only be 1 vector configured.
The max_qid, while 0-based, also needs to be 1 larger than the number
of (1-based) vectors, due to the admin queue and first I/O queue
sharing the first vector. So the 0-based max_qid is set to equal the
1-based number of vectors, resulting in the correct number of total
queues, which is 1 more than the total number of vectors, due to
the admin queue and first I/O queue sharing vector 0.
