nvme/pci: Fix read queue count

If nvme.write_queues equals the number of CPUs, the driver had decreased
the number of interrupts available such that there could only be one read
queue even if the controller could support more. Remove the interrupt
count reduction in this case. The driver wouldn't request more IRQs than
it wants queues anyway.

Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Keith Busch <kbusch@kernel.org>