hw/block/nvme: fix pci doorbell size calculation

hw/block/nvme: fix pci doorbell size calculation

The size of the BAR is 0x1000 (main registers) + 8 bytes for each
queue. Currently, the size of the BAR is calculated like so:

    n->reg_size = pow2ceil(0x1004 + 2 * (n->num_queues + 1) * 4);

Since the 'num_queues' parameter already accounts for the admin queue,
this should in any case not need to be incremented by one. Also, the
size should be initialized to (0x1000).

    n->reg_size = pow2ceil(0x1000 + 2 * n->num_queues * 4);

This, with the default value of num_queues (64), we will set aside room
for 1 admin queue and 63 I/O queues (4 bytes per doorbell, 2 doorbells
per queue).

Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Message-Id: <20200609190333.59390-2-its@irrelevant.dk>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>